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Organic amendments have been utilised as a source of nutrients to improve the growth and yield of many crops, including sweetpotato. However, none of the studies examined the relationship between organic amendments and the initiation of sweetpotato storage roots (SRs). A study was conducted in sweetpotato Orleans cultivar to investigate anatomical changes to roots during storage root formation aiming to elicit if organic amendment affects SR formation by changing soil available nitrogen (N) concentration. Two locally available organic amendments including poultry manure (PM) and sugarcane trash (SCT), were used in this experiment at different rates. Six treatments were included in the study: unamended soil (control), unamended soil with chemical fertiliser, PM 22 Mg/ha, PM 66 Mg/ha, SCT 10 Mg/ha and SCT 30 Mg/ha. Compared with unamended control, SCT application at both rates, 10 or 30 Mg ha−1, significantly promoted the formation of SRs and reduced root lignification, while PM amendment from 22 to 66 Mg ha−1 significantly inhibited SR initiation and enhanced the formation of lignified roots, which appear to be associated to high soil available N caused by PM addition. During the SR initiation, all amended treatments increased N accumulation in plants compared to the control. These results indicated that excessive soil available N introduced by PM amendment could inhibit the formation of SR of sweetpotato. Thus, when applying a lower rate of PM to sweetpotato, and planting should be delayed from 2 to 3 weeks after amending to avoid the detrimental effect on SR initiation. Excessively high rates of PM soil amendment (66 Mg ha−1) should be avoided. A suitable rate of SCT may be applied (~ 10 Mg ha−1 in this study) to promote SR formation of sweetpotato in soil with adequate available N level, but high rates could lead to immobilisation of N and suppress crop growth.

[Abstract] Two key hypotheses in invasion biology are that certain traits underlie invasiveness in introduced species, and that these traits are selected for during or after introduction. We tested these hypotheses by focusing on two traits likely to confer invasiveness, high increase in growth in response to increase in nutrients and low decrease in growth in response to competition. We compared four species of Carpobrotus that differ in invasiveness, using species from four continents: Africa, Australia, Europe and North America. To test for selection for these traits in Carpobrotus edulis, a highly invasive species, we compared plants from its native range in South Africa to plants from the other three regions, where C. edulis has been introduced. Plants were propagated in a common garden. Offspring were then grown alone with or without added nutrients, and together with another species of Carpobrotus or with the grass Ammophila arenaria (a co-occurring native species in Europe) without added nutrients. Response to nutrients did not differ between species of Carpobrotus, nor was competitive response less negative in more invasive species. However, increase in growth in response to added nutrients was greater in introduced than in native C. edulis. Moreover, fresh mass per ramet at the start of treatments was higher in the two invasive species than in the two non-invasive ones. We provide new evidence that introduction can select for response to nutrient enrichment in invasive species and add to the evidence for an association between size and invasiveness in introduced plants. [摘要] 四大洲食用昼花属的比较入侵生态学：对养分和竞争的响应 入侵生物学的两个关键假设是，某些特征是外来物种入侵的基础，且这些特征是在引入期间或之后选择的。我们通过关注两个可能赋予入侵性的特征来检验这些假设，即营养增加引起的较高生长加速和竞争引起的较低生长减速。我们对采自非洲、澳洲、欧洲和北美洲的4个食用昼花属(Carpobrotus)品 种进行了比较。为了测试高入侵物种莫邪菊(Carpobrotus edulis)对这些特征的选择，我们将原产于南非 的植株与入侵其他3个地区的植株进行了比较。在一个同质园中繁殖植株。然后，在添加或不添加养分的情况下单独培育子代，并在不添加养分的情况下将子代与另一个食用昼花属品种一起、或与欧洲的一种共生本土物种马兰草(Ammophila arenaria)一起培育。不同品种的食用昼花属对营养物质的反应并无差异，在入侵性更强的物种中，竞争反应的负面性也没有减弱。然而，与本土莫邪菊相比，添加营养物质引起外来莫邪菊更高的生长加速。此外，在处理开始时，两种入侵物种每分株的鲜质量高于两种非入侵物种。我们的研究结果表明，引种可以选择入侵物种对营养富集的反应进行选择，也证明了外来植物的体积和入侵性之间的关联。 Australian samples were collected under licenses SW018396 and CE005442 issued by the Western Australian Department of Parks and Wildlife. This paper is a contribution from the Alien Species Network (Ref. ED431D 2017/20—Xunta de Galicia, Autonomous Government of Galicia). Spanish Ministry of Economy and Competitiveness (Grant CGL2013-44519-R, co-financed by the European Regional Development Fund, to S.R.R.) and CSIRO Julius Career Award (to B.L.W.) Xunta de Galicia; ED431D 2017/20

Biochar can improve soil nutrient retention and alleviate salinity; however, use is not widespread due to cost. Biochar is usually co-applied with a full-rate of supplementary fertiliser before planting. This study investigated co-application of bamboo biochar with organic fertiliser and amendments on nutrient cycling, plant growth, yield and commercial value of ginger. Four treatments were applied including no amendment, organic amendments and organic amendments co-applied with biochar at two applications rates of 10 t ha−1 and 30 t ha−1. Plant growth, biomass, foliar nutrient and water-extractable soil nutrients were examined. Co-applied high rate biochar increased available soil potassium (K) concentration (+ 89%) over 22 weeks and led to increased foliar K concentration (+ 25%) at harvest and after 30 weeks compared with organic amendments alone. Biochar high rate decreased soil sodium concentration (− 22%) over 22 weeks. Biochar high rate increased root mass fraction and plant height but decreased the number of stems, and therefore, did not increase aboveground biomass compared with all other treatments. In contrast, ginger rhizome yield, grade and commercial value were not affected by biochar treatments. Added biochar provided additional net K that improved foliar concentration late in the growing season following dissolution. The additional K supply then stimulated root growth and biomass re-allocation despite daily irrigation throughout the growing season. Therefore, we suggest biochar as a useful amendment to prevent nutrient loss and alleviate salinity for organic crops.

Biochar has strong potential to improve nitrogen (N) use efficiency in both agricultural and horticultural systems. Biochar is usually co-applied with full rates of fertiliser. However, the extent to which N cycling can be affected after biochar application to meet plant N requirement remains uncertain. This study aimed to explore N cycling up to 2 years after biochar application. We applied pine woodchip biochar at 0, 10 and 30 t ha−1 (B0, B10, B30, respectively) in a macadamia orchard and evaluated the N isotope composition (δ15N) of soil, microbial biomass and macadamia leaves. Soil total N (TN) and inorganic N pools were also measured up to 2 years after biochar application. Biochar did not alter soil TN but soil NO3−-N increased at months 12 and 24 after biochar application. Soil NO3−-N concentrations were always over ideal levels of 15 μg g−1 in B30 throughout the study. Stepwise regression indicated that foliar δ15N decreases after biochar application were explained by increased NO3−-N concentrations in B30. Foliar TN and photosynthesis were not affected by biochar application. The soil in the high rate biochar plots had excess NO3−-N concentrations (over 30 μg g−1) from month 20 onwards. Therefore, N fertiliser applications could be adjusted to prevent excessive N inputs and increase farm profitability.

The aim of this meta-analysis and review study was to identify the original research works done on use of organic amendments against root-knot nematodes and to quantitatively analyse the effect of different organic amendment types, such as animal manure, composts, plant derivatives and plant residues, on root-knot nematodes in crops. The original studies conducted on RKN control using organic amendments were identified using database and literature searches. The articles were screened and data were extracted. The publication bias of the studies was calculated. The soil amendments used in experiments were identified into four main organic amendment categories: plant residues, composts, animal manure and plant derivatives (powders, pellets or extracts produced from plant or plant parts). A meta-analysis was performed calculating the response ratios (effect size) of different organic amendments against RKN favouring plant performances. All the amendment types, i.e. plant residues, composts, animal manures and plant derivatives, were found to be effective against RKN. Plant-based derivatives were the most effective against all RKN damage attributes followed by application of compost and animal manure. Poultry manure was the only effective animal manure to control RKN consistently based on the results. Plant residues were found to be the least effective against RKN; amongst these groups of organic amendments, the family Poaceae produced the most effective residues to control RKN. Organic amendment application generally reduced the RKN population and damage by 63 compared to untreated conditions.

The use of biochar is changing, and the combined application of biochar with fertilizer is increasingly gaining acceptance. However, the yield gains results reported in the existing literature through the co-application of fertilizer with biochar are conflicting. To resolve this, we utilized a meta-analysis of 627 paired data points extracted from 57 published articles to assess the performance of the co-application of biochar and fertilizers on crop yield compared with the corresponding controls. We also studied the impact of biochar characteristics, experimental conditions, and soil properties on crop yield. Our analysis showed that individually, biochar and inorganic fertilizer increased crop yield by 25.3% ± 3.2 (Bootstrap CI 95%) and 21.9% ± 4.4, respectively. The co-application of biochar with both inorganic and organic fertilizers increased crop yield by 179.6% ± 18.7, however, this data needs to be treated with caution due to the limited dataset. The highest yield increase was observed with amendments to very acidic soils (pH ≤5), but the benefits of biochar were not affected by the rate and the time after the application. In addition, the effects of biochar are enhanced when it is produced at 401–500 °C with a C:N ratio of 31–100. Our results suggest that the co-application of biochar with either inorganic and/or organic fertilizers in acidic soils increase crop productivity compared to amendment with either fertilizer or biochar. Our meta-analysis supports the utilization of biochar to enhance the efficiency and profitability of fertilizers.

• Here, we compared the carbon isotope ratios of leaf respiratory CO

This paper explores the potential of machine learning algorithms for weed and crop classification from UAV images. The identification of weeds in crops is a challenging task that has been addressed through orthomosaicing of images, feature extraction and labelling of images to train machine learning algorithms. In this paper, the performances of several machine learning algorithms, random forest (RF), support vector machine (SVM) and k-nearest neighbours (KNN), are analysed to detect weeds using UAV images collected from a chilli crop field located in Australia. The evaluation metrics used in the comparison of performance were accuracy, precision, recall, false positive rate and kappa coefficient. MATLAB is used for simulating the machine learning algorithms, and the achieved weed detection accuracies are 96% using RF, 94% using SVM and 63% using KNN. Based on this study, RF and SVM algorithms are efficient and practical to use, and can be implemented easily for detecting weed from UAV images.

Higher ecosystem nitrogen (N) inputs resulting from human activities often suppress soil microbial biomass and respiration, thereby altering biogeochemical cycling. Soil acidification and carbon (C) limitation may drive these microbial responses, yet their relative importance remains elusive, which limits our understanding of the longer-term effects of increasing N inputs. In a field experiment with continuous N addition at seven different rates from 0 to 50 g N m-2 yr-1 over six years in a temperate grassland of Inner Mongolia, China, we examined the responses of soil microbial biomass and respiration to changes in soil acidity and C availability by adding lime and/or glucose to soil samples. Soil microbial biomass and respiration did only weakly respond to increasing soil pH, but increased strongly in response to higher C availability with increasing N addition rates. Soil net N immobilization increased in response to glucose addition and soil microbial biomass increased at higher rates than microbial respiration along the gradient of previous N addition rates, both suggesting increasingly reinforced microbial C limitation with increasing N addition. Our results provide clear evidence for strong N-induced microbial C limitation, but only little support for soil acidity effects within the initial pH range of 4.73 to 7.86 covered by our study. Field data support this conclusion by showing reduced plant C allocation belowground in response to N addition, resulting in soil microbial C starvation over the long term. In conclusion, soil microbial biomass and respiration under N addition were strongly dependent on C availability, most likely originating from plant belowground C inputs, and was much less affected by changes in soil pH. Our data help clarify a long-standing debate about how increasing N input rates affect soil microbial biomass and respiration, and improve the mechanistic understanding of the linkages between ecosystem N enrichment and C cycling.

Smart farming has become imperative these days due to competition, and use of Unmanned Aerial Vehicle (UAV) imagery is becoming an integral part of the process. Machine learning techniques have been successfully applied to capture UAV imagery of various spectral bands to identify weed infestations. Identification of weeds in chilli crop is a challenging task. In this paper, RGB images captured by drones have been used to detect weed in chilli field. This task has been addressed through orthomasaicking of images, feature extraction, labelling of images to train machine learning algorithms, and use of unsupervised learning with random forest for classification. MATLAB has been used for all computations and out-of-bag accuracy achieved for identifying weeds is 96\(\%\).

A number of published studies have focused on the effects of N application timing on sweetpotato yield. However, none of them examined the influence of the timing of N fertilisation on the initiation of storage roots (SRs), which largely determines the number of tubers per plant and substantially affect the yield. A pot experiment was conducted in sand culture to evaluate the influence of N application timing (N applied on the planting day, 3, 7 and 14 days after transplanting (DAT), denoted T1, T3, T7 and T14, respectively, and a no N applied control T0) on the plant acquisition of N and the initiation of SRs of ‘Orleans’ cultivar. A previously-determined optimal N rate for the SR formation (Hoagland solution with 100mg/L N) in the experimental system was used. Rapid SR formation was found to require N during the first week after transplanting. No or late N application delayed the initiation of SRs and reduced the number of SRs. No or delayed N application inhibited the formation of regular vascular cambium (RVC) and anomalous cambium (AC) and led to an increase in lignification of stele cells leading to significantly higher proportion of lignified roots. By contrast, plants supplied with N within 7 DAT had a higher rate of SRs and lower rate of lignified roots. Also, earlier N application promoted total plant and root growth measured as higher biomass and storage root weight, as well as higher N accumulation in plants and higher nitrogen recovery efficiency (NRE). Results suggested that the SR formation required N during the first week after transplanting. Therefore, moderate N should be available in soil before or on planting day.

Biochar compound fertilisers (BCFs) are an emerging technology that combine biochar with nutrients, clays and minerals and can be formulated to address specific issues in soil-plant systems. However, knowledge of BCF performance over consecutive crops and without re-application is limited. This study aims to assess the residual effect of organic BCFs soil-plant nutrient cycling 2 years after application and without additional fertiliser inputs. We applied BCFs and biochar with organic fertiliser amendments and established a crop of ginger and a second crop of turmeric (Curcuma longa) without re-application or additional fertilisation. All treatment formulations included bamboo-biochar and organic fertiliser amendments; however, two novel BCFs were formulated to promote agronomic response in an intensive cropping system. We report here on the effect of treatments on soil and plant macronutrient and micronutrient cycling and turmeric growth, biomass and yield at harvest. Both BCFs (enriched (10 t ha-1) and organo-mineral biochar (8.6 t ha-1) increased foliar K (+155% and +120%) and decreased foliar Mg (-20% and -19%) concentration compared with all other treatments, suggesting antagonism between K and Mg. Plants were limited for K, P and B at harvest but not N, Ca or Mg. Foliar K was dependent on the biochar formulation rather than the rate of application. Biochar-clay aggregates increased K retention and cycling in the soil solution 2 years after application. Clay blended BCFs reduced K limitation in turmeric compared to biochar co-applied with organic amendments, suggesting these blends can be used to manage organic K nutrition. All formulations and rates of biochar increased leaf biomass and shoot-to-root ratio. Novel BCFs should be considered as an alternative to co-applying biochar with organic fertiliser amendments to decrease application rates and increase economic feasibility for farmers. Applying BCFs without re-application or supplementary fertiliser did not provide sufficient K or P reserves in the second year for consecutive cropping. Therefore, supplementary fertilisation is recommended to avoid nutrient deficiency and reduced yield for consecutive organic rhizome crops.

Natural initiation of pineapple flowers is not synchronized, which yields difficulties in yield prediction and the decision of harvest. Computer vision based pineapple detection system is an automated solution to address this issue. However, it is faced with significant challenges, e.g. pineapple flowers and fruits vary in size at different growing stages, the images are influenced by camera viewpoint, illumination conditions, occlusion and so on. This paper presents an approach for pineapple fruit and flower recognition using a state-of-the-art deep object detection model. We collected images from pineapple orchard using three different cameras and selected suitable ones to create a dataset. The experimental results show promising detection performance, with an mAP of 0.64 and \(F_1\) score of 0.69.

Biochar has agronomic potential but currently is too expensive for widespread adoption. New methodologies are emerging to reduce the cost such as enriching biochar with nutrients that match crops and soil requirements. However, the effects of biochar-based fertilisers on plant yield and soil nutrient availability have not been widely examined. This study investigated the effects of a novel organo-mineral biochar fertiliser in comparison to organic and commercial biochar fertiliser on ginger (Zingiber officinale Canton). There were four treatments: (1) commercial organic fertiliser (5 t ha−1), as the control; (2) commercial biochar-based fertiliser (5 t ha−1); (3) organo-mineral biochar fertiliser at low rate (3 t ha−1); and (4) organo-mineral biochar fertiliser at high rate (7.5 t ha−1). A replicated pot trial was established with black dermosol soil and ten replicate pots for each treatment. Ginger was planted and grown for 30 weeks. Plant growth, biomass, foliar nutrients and water extractable soil nutrients including phosphorus (P), potassium (K) and calcium (Ca) were examined. High rate organo-mineral biochar fertiliser increased soil P and K availability at week 30 (harvest) after planting, compared to all other treatments and low rate organo-mineral biochar fertiliser performed similarly to the organic control for P and K. High rate organo-mineral biochar fertiliser increased total foliar nutrient content at week 30 in P, K and Ca compared to commercial biochar fertiliser. High rate organo-mineral biochar fertiliser improved the commercial value of ginger (+ 36%) due to a shift in the proportion of higher grade rhizomes. Low rate organo-mineral biochar fertiliser plants displayed similar yield, total dry and aboveground biomass to commercial organic fertiliser. Commercial biochar fertiliser had significantly lower biomass measures compared with other treatments as the rate applied had lower nutrient concentrations. Our results show organo-mineral biochar fertilisers could be substituted for commercial organic fertilisers at low rates to maintain similar yield or applied at high rates to increase commercial value where economically feasible.

As a climate change mitigation strategy, biochar application to soil has been demonstrated to increase soil carbon (C) sequestration and reduce greenhouse gas (GHG) emission. Although numerous manipulative studies have been conducted, it is still not fully understood how biochar application affects soil respiration ( Rs ) and its components (i.e., autotrophic [ Ra ] and heterotrophic respiration [ Rh ]) in forest ecosystems, especially in subtropical forests. In this study, we performed a meta-analysis of forest ecosystems and a field experiment with biochar amendments of 0, 10, and 30 t ha −1 in a subtropical forest in Zhejiang, China to examine the effects of biochar application on Rs and its components. Our results showed that biochar application significantly increased Rs by 20.92% at the global scale with an increase of 20.25% in temperate forests and a nonsignificant effect in subtropical forests. Responses of Rs to biochar application varied with experimental methods and soil textures. Similarly, our field experiment showed that biochar amendment did not significantly affect Ra, Rh , and Rs in a subtropical forest in Eastern China. Specifically, the average Rs under biochar amendments of 0, 10, and 30 t ha −1 were 2.37, 2.06 and 2.15 μmol m −2 s −1 , respectively ( P > 0.05). Both Rs and Rh were positively correlated with microbial biomass C (MBC) and negatively with dissolved organic C (DOC). Both apparent temperature sensitivity ( Q 10 ) of Rh and Rs were significantly higher under biochar treatments than in the control. Our findings indicate the importance of the differential effects of biochar application on Rs in different forest types for C sequestration, which may inform ecosystem and regional models to improve prediction of biochar effects on forest C dynamics and climate-biosphere feedbacks.

General circulation models predict that precipitation will become more extreme, i.e. rainfall events of larger size but reduced frequency. Studies in North American grasslands have shown that such repackaging of precipitation into fewer, larger events enhanced above ground net primary productivity (ANPP), likely due to deeper soil moisture infiltration favoring plant water use over evaporation. However, ANPP responses in other regions remain poorly understood, and responses of carbon and water exchanges with the atmosphere remain unknown. Here we manipulated rainfall in a steppe ecosystem of northern China over 4 years to investigate how temporal packaging of precipitation impacts ANPP, evapotranspiration (ET), net ecosystem CO2 exchange (NEE) and the component fluxes gross primary productivity (GPP) and ecosystem respiration (RE). Experimental plots received precipitation equivalent to the 60-year growing-season average of 240 mm, variously packaged into 6, 10, 16, or 24 events representing extreme (P6) to historical average (P24) rainfall frequency. Extraordinarily extreme frequency (6 large events) reduced NEE, GPP, RE, ET and water use efficiency (WUE = |NEE|/ET). The average NEE, GPP and RE declined 35%, 45% and 48% respectively in the P6 treatment as compared to P16, which showed maximum ET and CO2 exchange. After peaking in the 16-event treatment, GPP and WUE in P24 were not distinguishable from P6. These peaks suggest that P16 was optimal for photosynthesis, with sufficiently frequent rain to maintain unregulated plants and adequately deep soil moisture infiltration to favour transpiration, with associated carbon uptake, over evaporation. Path analysis indicated the lower CO2 fluxes were influenced by reduced soil water content and leaf area index and higher soil temperature, with ET regulating the effects of these microclimatic drivers. ANPP showed a monotonic but non-significant decline with decreasing precipitation frequency, consistent with reduced CO2 fluxes. We found an increase in ANPP of xerophyte plants partially compensated for the ANPP decline in the dominant eurytopic xerophyte plants. Our results suggest that extreme temporal repackaging of precipitation into few events with correspondingly long dry intervals may reduce the capacity of steppe ecosystems to assimilate atmospheric CO2, although community diversity may moderate impacts.

Root-knot nematodes (Meloidogyne spp.) are considered as the most serious nematode pest in the world and have been reported to cause up to 57–67 % crop yield losses in untreated conditions in Australia. Chemical control has been the most popular method to manage root-knot nematodes due to its high efficacy. However, ‘fenamiphos’ the most widely used active ingredient in nematicides, has recently been reviewed by the Australian Pesticides and Veterinary Medicines Authority and subsequently has been recommended for removal from the commercial market in Australia due to concerns about its potential to contribute to adverse environmental and human health impacts. Due to this pressure of nematicide restrictions, alternative chemical and organic formulations were assessed against root-knot nematodes in a sweetpotato field trial comparing with untreated control and chemical control ‘oxamyl’ (currently registered chemical for sweetpotato). Fluensulfone significantly reduced soil root-knot nematode numbers compared to other treatments, giving the highest marketable yield in this trial. Abamectin did not give significant root-knot nematode control or damage reduction. Organic nematicide treatments (garlic formulation and nutrient and microbial formulation) did not show a significant reduction of soil root-knot nematode numbers and root damage. No significant effect of nematicides was found on non-target organisms (soil bacteria and nematodes) at 24 weeks after planting.

Organo-mineral biochar fertiliser has the potential to replace conventional biochar and organic fertiliser to improve soil quality and increase plant photosynthesis. This study explored mechanisms involved in nitrogen (N) cycling in both soil and ginger plants (Zingiber officinale: Zingiberaceae) following different treatments including organic fertiliser, commercial bamboo biochar fertiliser, and organo-mineral biochar fertiliser. Soil received four treatments including (1) commercial organic fertiliser (5 t ha−1) as the control, (2) commercial bamboo biochar fertiliser (5 t ha−1), (3) organo-mineral biochar fertiliser at a low rate (3 t ha−1), and (4) organo-mineral biochar fertiliser at a high rate (7.5 t ha−1). C and N fractions of soil and plant, and gas exchange measurements were analysed. Initially, organo-mineral biochar fertiliser applied at the low rate increased leaf N. Organo-mineral biochar fertiliser applied at the high rate significantly increased N use efficiency (NUE) of the aboveground biomass compared with other treatments and improved photosynthesis compared with the control. There was N fractionation during plant N uptake and assimilation since the 15N enrichment between the root, leaf, and stem were significantly different from zero; however, treatments did not affect this N fractionation. Organo-mineral biochar fertiliser has agronomic advantages over inorganic and raw organic (manure-based) N fertiliser because it allows farmer to put high concentrations of nutrients into soil without restricting N availability, N uptake, and plant photosynthesis. We recommend applying the low rate of organo-mineral biochar fertiliser as a substitute for commercial organic fertiliser.

Global climate change is projected to increase both the intensity and frequency of extreme precipitation events (EPEs), which are considered to have stronger impacts on ecosystem functions than gradual changes in mean precipitation conditions. In this study, a consecutive 20-day extreme precipitation event (282 mm) was applied during the mid- and late-growing season periods in a semiarid steppe for three years to investigate the effects of extreme large precipitation events on aboveground net primary productivity (ANPP) and ecosystem carbon dioxide (CO 2 ) fluxes, including net ecosystem carbon absorption (NEE), gross primary productivity (GPP) and ecosystem respiration (Re). Although soil moisture was significantly increased by extreme precipitation, and even exceeded field capacity during the treatment periods, ANPP remained stable across all the treatments. There was also little change in mean growing season ecosystem CO 2 fluxes under the two precipitation treatments, despite GPP rates decreased by 34.4 and 26.3%, and NEE rates were suppressed by 77 and 68% during the mid- and late-season treatment periods, respectively. The stable CO 2 fluxes could be attributed to the recovery of GPP and NEE in 7 and 12 days after the end of EPEs. Our study demonstrated that both ANPP and CO 2 fluxes in this semiarid steppe were very stable in the face of extreme large precipitation events, regardless of the timing of events occur. Nevertheless, future, long-term studies need to investigate the potential tipping points or thresholds for ecosystem function shifts, as an increasing occurrence of EPEs has been forecasted in future climate change scenarios.

The interaction between biochar and soil changes nitrogen (N) dynamics in different ecosystems. Although multiple studies have reported influences of biochar on soil inorganic N (SIN) including ammonium (NH4+-N) and nitrate (NO3−-N), the influences reported are contradictory. We undertook a meta-analysis to investigate how biochar properties and the interaction among biochar, soil and fertilisation affect SIN. This quantitative analysis used 56 studies with 1080 experimental cases from manuscripts published between 2010 and 2015. Overall, we found that biochar reduced SIN regardless of experimental conditions (approximately − 11 ± 2% of NH4+-N and − 10 ± 1.6% of NO3−-N); however, 95% of cases were observed within one year after biochar application. SIN was best explained by residence time of biochar in soil, pyrolysis temperature, application rate, fertiliser type, and soil pH. The effects of biochar were complex due to the interaction of biochar with environmental factors. Most biochar trials used wood as a feedstock, but woody biochar did not decrease SIN as much as other plant-derived biochars. When biochar was used with NH4-based fertilisers, SIN decreased compared to biochar with no fertiliser. In contrast, adding organic fertiliser with biochar increased SIN compared to biochar alone. SIN was clearly reduced after one month of biochar application, suggesting that biochar should be applied at least one month prior to planting so plants are not affected by decreased N. Our results revealed that the interactions between biochar and environmental factors, pyrolysis temperature of biochar and biochar surface properties are the main driving factors affecting SIN. There were limited long-term studies of > 1 year, thus the long-term effects of biochar on SIN still remain unclear.

Disturbances usually initiate processes of fragmentation in clonal plants, with the consequent division into portions of different size. The ability of these portions to survive and regrow after fragmentation plays an important role in the maintenance of populations and the colonization of new environments. In this field experiment we aim to determine the importance of stolons as reserve organs in the colonization of a coastal sand dune by a clonal invader. We simulated an event of fragmentation of clones of an aggressive invader into portions with short and long stolon sizes. Our results showed a reduction of biomass allocation to roots in the long stolon treatment that was balanced by an increase in the above-ground growth; consequently, the area colonized by the invader was greater. We report evidence that stolons can contribute to buffering stressful conditions and allow expansion of the invader into a natural coastal sand dune.

Climate extremes are expected to increase in frequency and intensity as a consequence of anthropogenic climate change attributed to the rise of atmospheric concentrations of greenhouse gases (GHGs). However, studies on the impacts of climate extremes on terrestrial ecosystems are limited. Here, we experimentally imposed extreme drought and a heat wave (∼60-year recurrence) to investigate their effects on GHGs fluxes of a semiarid grassland in China. We estimated a 16% and 38% percent reduction in net ecosystem CO2 uptake caused by the heat wave and drought respectively, but via different mechanisms. Drought reduced gross ecosystem productively (GEP) and to a lower extent ecosystem respiration (ER). By contrast, the simulated heat wave suppressed only GEP while ER remained stable. The climate extremes also created a legacy effect on GEP and NEE lasting until the end of the growing season, whereas ER recovered immediately. Although CH4 and N2O fluxes were unaffected by the heat wave, drought promoted CH4 uptake and suppressed N2O emission during the treatment period. The effect of drought on GHGs fluxes generally overwhelmed that of the heat wave treatment, and there were no interactive effects of these two types of climate extremes. Our results showed that responses of ecosystem GHGs exchange to climate extremes are strongly regulated by soil moisture status. In conclusion, future amplification of climate extremes could decrease the sink for GHGs, especially CO2, in this semiarid grasslands.

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gases (GHGs) fluxes appear variable among many case studies; therefore the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta-analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture, and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate and latitude also influence soil GHG fluxes, but to a more limited extent.Our findings provide a scientific basis for developing more rational strategies towards widespread adoption of biochar as a soil amendment for climate change mitigation;

Sustainable nut production and supply depend on soil nutrient availability, but current land management practices in macadamia farms, including soil erosion and minimal inter row groundcover in established orchards can reduce soil carbon (C) and impair soil fertility. Therefore, nut production in macadamia orchards relies heavily on inorganic and organic fertiliser application which brings an economic burden for farmers. Biochar, a C rich product from the pyrolysis of organic residues, has been shown to improve soil fertility and fertiliser use efficiency. In the current study, we aimed to explore the effects of a wood-based biochar at two application rates of 10 t ha-1 (B10) and 30 t ha-1 (B30) on soil C and nitrogen (N) cycling at months 0, 6, 12, 18 and 24 following its application to a macadamia orchard. No significant effects of biochar on soil soluble organic C and N were observed at months 0, 6 and 12 following biochar application. At months 12, 18 and 24, biochar significantly increased soil nitrate concentration with B30 compared to the control and B10 but differences were significant only at month 12.;

Epigenetic variation may play an important role in how plants cope with novel environments. While significant epigenetic differences among plants from contrasting habitats have often been observed in the field, the stability of these differences remains little understood. Here, we combined field monitoring with a multi-generation common garden approach to study the dynamics of DNA methylation variation in invasive Chinese populations of the clonal alligator weed (Alternanthera philoxeroides). Using AFLP and MSAP markers, we found little variation in DNA sequence but substantial epigenetic population differentiation. In the field, these differences remained stable across multiple years, whereas in a common environment they were maintained at first but then progressively eroded. However, some epigenetic differentiation remained even after 10 asexual generations. Our data indicate that epigenetic variation in alligator weed most likely results from a combination of environmental induction and spontaneous epimutation, and that much of it is neither rapidly reversible (phenotypic plasticity) nor long-term stable, but instead displays an intermediate level of stability. Such transient epigenetic stability could be a beneficial mechanism in novel and heterogeneous environments, particularly in a genetically impoverished invader.

It has recently been hypothesised that ethylene, released into soil by stressed plants, reduces the oxidation of methane by methanotroph. To test this, a field trial was established in which maize plants were grown with and without soil moisture stress, and the effects of addition aminoethoxyvinylglycine (AVG; an ethylene biosynthesis inhibitor), and biochar (increases soil water holding capacity and reduces plant stress) were determined following the static incubation of soil samples. AVG increased methane oxidation rates by 50 % (P = 0.039), but only in the absence of irrigation. No other treatment effects were observed. This result provides evidence for a positive feedback system between plant stress, ethylene production, and impacts on methanotrophic activity.

Biochar has been shown to affect soil microbial diversity and abundance. Soil microbes play a key role in soil nutrient cycling, but there is still a dearth of knowledge on the responses of soil microbes to biochar amendments, particularly for longer-term or repeated applications. We sampled soil from a field trial to determine the individual and combined effects of newly applied (1 year ago), re-applied (1 year ago into aged biochar) and aged (9 years ago) biochar amendments on soil bacterial communities, with the aim of identifying the potential underlying mechanisms or consequences of these effects. Soil bacterial diversity and community composition were analysed by sequencing of 16S rRNA using a Miseq platform. This investigation showed that biochar in soil after 1 year significantly increased bacterial diversity and the relative abundance of nitrifiers and bacteria consuming pyrogenic carbon (C). We also found that the reapplication of biochar had no significant effects on soil bacterial communities. Mantel correlation between bacterial diversity and soil chemical properties for four treatments showed that the changes in soil microbial community composition were well explained by soil pH, electrical conductivity (EC), extractable organic C and total extractable nitrogen (N). These results suggested that the effects of biochar amendment on soil bacterial communities were highly time-dependent. Our study highlighted the acclimation of soil bacteria on receiving repeated biochar amendment, leading to similar bacterial diversity and community structure among 9-years old applied biochar, repeated biochar treatments and control.

Biochar has excellent potential to improve crop yield and quality, but its effects vary depending on soil type and agronomic inputs (e.g., irrigation and fertiliser). In this study, we investigate the effects of biochar on peanut productivity and crop quality under different irrigation and fertilisation regime in red Ferrosols. We applied peanut shell biochar (9.2 t ha−1) on a red Ferrosol under field conditions to examine the effects of biochar, irrigation, fertiliser and their interactions on soil properties and yield and kernel quality of the peanut variety ‘Middleton’. Biochar application improved kernel quality by increasing the fraction of the highest commercial grade kernels (grade ‘Jumbo’) but did not affect photosynthesis and yield of peanut. Biochar application also increased soil total C (TC), total nitrogen (TN) and C/N ratio, and changed soil C and N stable isotope composition. Soil K and Zn content was higher in biochar treatments, which partially explains the observed kernel grade improvement. Fertilisation did not improve peanut performance, and irrigation generally had a negative effect on crop yield and physiology, but these data were compromised by high rainfall during cropping. There were few interactions among biochar, irrigation and fertiliser treatments. Peanut shell biochar improves soil organic C, nutrient availability and peanut kernel quality under different irrigation and fertiliser rate regimes in field conditions.

Forest recovery has been extensively evaluated using plant communities but fewer studies have been conducted on soil fauna. This study reports the status of soil nematode communities during natural re-establishment after deforestation in a subtropical forest in southwestern China. Soil nematode communities of two secondary succession stages, shrub-grassland and secondary forest, were compared with those of virgin forest. Shrub-grassland had higher herbivore relative abundance but lower fungivore and bacterivore relative abundance than forests. Between secondary and virgin forest, the latter had higher abundance of bacterivores. Shrub-grassland had lower nematode diversity, generic richness, maturity index and trophic diversity index than virgin forest, whereas there were no differences in these indices between secondary forest and virgin forest. The small differences in nematode community structures between secondary forest and virgin forest suggest that soil nematode communities recovered to a level close to that of the undisturbed forest after up to 50 years of natural succession.

Biochar has significant potential to improve crop performance. This study examined the effect of biochar application on the photosynthesis and yield of peanut crop grown on two soil types. The commercial peanut cultivar Middleton was grown on red ferrosol and redoxi-hydrosol (Queensland, Australia) amended with a peanut shell biochar gradient (0, 0.375, 0.750, 1.50, 3.00 and 6.00%, w/w, equivalent up to 85 t ha(-1)) in a glasshouse pot experiment. Biomass and pod yield, photosynthesis-[CO2] response parameters, leaf characteristics and soil properties (carbon, nitrogen (N) and nutrients) were quantified. Biochar significantly improved peanut biomass and pod yield up to 2- and 3-folds respectively in red ferrosol and redoxi-hydrosol. A modest (but significant) biochar-induced improvement of the maximum electron transport rate and saturating photosynthetic rate was observed for red ferrosol. This response was correlated to increased leaf N and accompanied with improved soil available N and biological N fixation. Biochar application also improved the availability of other soil nutrients, which appeared critical in improving peanut performance, especially on infertile redoxi-hydrosol. Our study suggests that application of peanut shell derived biochar has strong potential to improve peanut yield on red ferrosol and redoxi-hydrosol. Biochar soil amendment can affect leaf N status and photosynthesis, but the effect varied with soil type.

Alligator weed, Alternanthera philoxeroides (Mart.) Griseb., is one of the worst invasive weeds in the world. In the present study, the genome size of seven forms/biotypes of alligator weed from Argentina (native area), the USA (introduced area), and China (introduced area) was analyzed using flow cytometers; the ribosomal DNA internal transcribed spacer region (ITS) was cloned and sequenced. We found that the genome size of A. philoxeroides ranged from 5.72 to 8.50 pg/2C nucleus, consisting of four levels of genome and three kinds of ploidy. Among them, three levels and two kinds (tetraploid and hexaploid) were found in samples from Argentina, two levels and one kind (pentaploid) in US samples, and one level and one kind (hexaploid) in samples from China. Contrary to the significant variation in genome size, we found that the intraspecific differentiation of the ITS sequences in the seven forms/biotypes was extremely low, and that six of them shared ITS sequences with no or one single substitution. These results show that the change of genome size played a major role in the differentiation of A. philoxeroides, and that forms/biotypes with higher ploidy seem to have stronger invasive ability. Furthermore, the differences of A. philoxeroides in ploidy between samples from the USA and China showed that alligator weeds from these two invaded areas certainly have different native progenitors.

Climate change is likely to increase both intensity and frequency of drought stress. The responses of soil respiration (R s) and its components (root respiration, R r; mycorrhizal respiration, R m; and heterotrophic respiration, R h) to drought stress can be different. This work aims to review the recent and current literature about the variations in R s during the period of drought stress, to explore potential coupling processes and mechanisms between R s and driving factors in the context of global climate change. The sensitivity of soil respiration and its components to drought stress depended on the ecosystems and seasonality. Drought stress depressed R s in mesic and xeric ecosystems, while it stimulated R s in hydric ecosystems. The reductions in supply and availability of substrate decreased both auto- and heterotrophic respirations, leading to the temporal decoupling of root and mycorrhizal respiration from canopy photosynthesis as well as C allocation. Drought stress also reduced the diffusion of soluble C substrate, and activities of extracellular enzymes, consequently, limited microbial activity and reduced soil organic matter decomposition. Drought stress altered Q 10 values and broke the coupling between temperature and soil respiration. Under drought stress conditions, R m is generally less sensitive to temperature than R r and R h. Elevated CO2 concentration alleviated the negative effect of drought stress on soil respiration, principally due to the promotion of plant C assimilation subsequently, which increased substrate supply for respiration in both roots and soil microorganisms. Additionally, rewetting stimulated soil respiration dramatically in most cases, except for soil that experienced extreme drought stress periods. The legacy of drought stress can also regulate the response of soil respiration rate to rewetting events in terrestrial ecosystems through changing abiotic drivers and microbial community structure. There is increasing evidence that drought stress can result in the decoupling of the above- and belowground processes, which are associated with soil respiration. However, studies on the variation in rates of soil respiration and its components under different intensities and frequencies of drought stress over the ecosystems should be reinforced. Meanwhile, molecular phylogenetics and functional genomics should be applied to link microbial ecology to the process of R s. In addition, we should quantify the relationship between soil respiration and global change parameters (such as warming and elevated [CO2]) under drought stress. Models simulating the rates of soil respiration and its components under global climate change and drought stress should also be developed.

Phenotypic plasticity has been proposed as an important adaptive strategy for clonal plants in heterogeneous habitats. Increased phenotypic plasticity can be especially beneficial for invasive clonal plants, allowing them to colonize new environments even when genetic diversity is low. However, the relative importance of genetic diversity and phenotypic plasticity for invasion success remains largely unknown. Here, we performed molecular marker analyses and a common garden experiment to investigate the genetic diversity and phenotypic plasticity of the globally important weed Alternanthera philoxeroides in response to different water availability (terrestrial vs. aquatic habitats). This species relies predominantly on clonal propagation in introduced ranges. We therefore expected genetic diversity to be restricted in the two sampled introduced ranges (the USA and China) when compared to the native range (Argentina), but that phenotypic plasticity may allow the species' full niche range to nonetheless be exploited. We found clones from China had very low genetic diversity in terms of both marker diversity and quantitative variation when compared with those from the USA and Argentina, probably reflecting different introduction histories. In contrast, similar patterns of phenotypic plasticity were found for clones from all three regions. Furthermore, despite the different levels of genetic diversity, bioclimatic modeling suggested that the full potential bioclimatic distribution had been invaded in both China and USA. Phenotypic plasticity, not genetic diversity, was therefore critical in allowing A. philoxeroides to invade diverse habitats across broad geographic areas. Fil: Geng, Yupeng. Yunnan University; China. Fudan University; China Fil: van Klinken, Rieks D.. Csiro Ecosystem Sciences; Australia Fil: Sosa, Alejandro Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación para el Estudio de Especies Invasivas; Argentina Fil: Li, Bo. Fudan University; China Fil: Chen, Jiakuan. Central Queensland University; Australia Fil: Xu, Cheng Yuan. Central Queensland University; Australia

The rise in atmospheric [CO(2)] is associated with increasing air temperature. However, studies on plant responses to interactive effects of [CO(2)] and temperature are limited, particularly for leaf structural attributes. In this study, Eucalyptus saligna plants were grown in sun-lit glasshouses differing in [CO(2)] (290, 400, and 650 µmol mol(-1)) and temperature (26 °C and 30 °C). Leaf anatomy and chloroplast parameters were assessed with three-dimensional confocal microscopy, and the interactive effects of [CO(2)] and temperature were quantified. The relative influence of leaf structural attributes and chemical properties on the variation of leaf mass per area (LMA) and photosynthesis within these climate regimes was also determined. Leaf thickness and mesophyll size increased in higher [CO(2)] but decreased at the warmer temperature; no treatment interaction was observed. In pre-industrial [CO(2)], warming reduced chloroplast diameter without altering chloroplast number per cell, but the opposite pattern (reduced chloroplast number per cell and unchanged chloroplast diameter) was observed in both current and projected [CO(2)]. The variation of LMA was primarily explained by total non-structural carbohydrate (TNC) concentration rather than leaf thickness. Leaf photosynthetic capacity (light- and [CO(2)]-saturated rate at 28 °C) and light-saturated photosynthesis (under growth [CO(2)] and temperature) were primarily determined by leaf nitrogen contents, while secondarily affected by chloroplast gas exchange surface area and chloroplast number per cell, respectively. In conclusion, leaf structural attributes are less important than TNC and nitrogen in affecting LMA and photosynthesis responses to the studied climate regimes, indicating that leaf structural attributes have limited capacity to adjust these functional traits in a changing climate.

Age-related reductions in stand biomass accumulation are frequently observed in old-growth forests. The phenomenon may be caused by reduced production, increased mortality or both. The relative importance of production and mortality is not well studied, so the mechanisms controlling age-related decline of stand biomass accumulation remain unclear. In this study, conducted in a Quercus-dominated deciduous forest in the Northeastern USA, we examined whether age-related decline in stand above-ground biomass (AGB) accumulation could be explained by reduction of above-ground net primary production (NPP) (growth of surviving trees) that may be associated with (i) physiological constraints within individual trees or (ii) changes in stand structure, or by (iii) age-related, increasing tree mortality in stands up to 135years old. Few previous studies have tested these hypotheses simultaneously within the same forest. We did not find evidence for a reduction in individual tree growth associated with age-related physiological constraints, in terms of foliar carbon assimilation capacity, photosynthesis/respiration balance, nitrogen availability or hydraulic constraints on carbon gain. Over the period of 1937-2006, we did not observe alterations in stand structure, and the above-ground NPP of the Quercus forest was generally stable. However, we did find that the primary mechanism driving age-related decline of stand AGB accumulation was biomass loss due to the death of large, dominant trees. Our results indicate that shifts in mortality from the loss of small trees to the loss of large trees, rather than changes in above-ground NPP, drives age-related decline in stand AGB accumulation in this forest. Synthesis.We found that within the range of stand development stages analysed, the age-related decline of stand AGB accumulation in a Quercus-dominated forest was primarily due to mortality of large, dominant trees and not due to changes in above-ground NPP associated with tree physiology, individual tree growth or stand structure. This result indicates that tree demography and the influence of climate change on disturbances may need to be integrated into models to predict the change of above-ground carbon stock of some old-growth forests.

Clonal plants benefit from the ability to translocate resources among interconnected ramets to colonize heterogeneous habitats. Clonal integration affects the resource level and morphological traits of ramets, and thus may influence their physiology and general performance. Although leaf gas exchange and its associated physiological adjustments are key traits to assess plant fitness, the effect of clonal integration on these functional traits is insufficiently understood. 2. In a glasshouse experiment, we addressed how clonal integration affects gas exchange properties, leaf characters and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under full sun and 85%shade. We also used stable-isotope labelling to assess the maternal subsidy to daughter ramets. 3. Similar effects of connection were observed in both species for most gas exchange parameters and leaf characters. Clonal integration did not affect photosynthetic capacity and respiratory rates of ramets.When grown in shade, ramets connected with an unshaded mother plant displayed higher area-based leaf nitrogen and chlorophyll content than severed ramets, but the additional nitrogen and chlorophyll was not translated to increased photosynthetic capability. Overall, severed ramets displayed significant light response for leaf nitrogen (area-based), photosynthetic nitrogen use efficiency, chlorophyll to nitrogen ratio, and nitrogen stable-isotope signature, but the light response was eliminated by clonal integration in connected ramets. 4. Both species displayed substantial maternal carbohydrate subsidy that benefited the growth of daughter ramets, but species-specific patterns were observed in the growth of daughter ramets and the amount of subsidy. The amount of subsidy was independent of ramet growth light levels for P. canescens, but shaded, connected ramets of A. philoxeroides received more subsidy than unshaded controls, facilitating a larger growth improvement relative to severed counterparts than P. canescens. 5. Synthesis. We observed increased leaf nitrogen and chlorophyll in shaded, connected ramets of two clonal invasive plants. Clonal integration may facilitate nitrogen assimilation and allow preacclimation to high-light conditions for shaded, connected ramets, thus promoting the opportunistic expansion of these invaders on site scale. The species-specific maternal subsidy pattern demonstrated that clonal plants possess different strategies to subsidize ramets under light-limited conditions.

The deciduous forests of northeastern United States are currently experiencing an invasion of the exotic plant species Japanese barberry (Berberis thunbergii). This recent and rapid invasion leads to rising concern about its potential threats to native species as well as natural ecosystems, demanding a better understanding of its invasion mechanisms and potential responses to climate change. Unfortunately, few studies have been conducted to understand the influence of climate on the growth of B. thunbergii, largely because of the absence of long-term growth records. In this study we demonstrate growth rings of B. thunbergii are annually resolved and crossdatable. The first ring-width chronology of B. thunbergii was therefore developed using samples collected from the Black Rock Forest (BRF), New York. Climate-growth relationship analysis indicates the growth of B. thunbergii in the BRF is positively correlated with precipitation in prior October, current February and May–August, but is negatively...

Stand-level, canopy foliar carbon loss (R(can)) was modeled for a virtual Quercus rubra L. monoculture at two sites differing in soil water availability in a northeastern deciduous forest (USA) throughout the 2003 growing season. Previously reported foliar respiratory temperature responses of Q. rubra were used to parameterize a full distributed physiology model that estimates R(can) by integrating the effects of season, site and canopy position, and represents the best estimation of R(can). Model sensitivity to five simplified parameterization scenarios was tested, and a reasonable procedure of simplification was established. Neglecting effects of season, site or canopy position on respiration causes considerable relative error in R(can) estimation. By contrast, assuming a constant E(0) (a temperature response variable of the respiration model), or a constant night temperature (mean nighttime temperature) caused only a small relative error (< 10%) compared with the full model. From June 8 to October 28, 2003, modeled R(can) of the virtual Q. rubra monoculture was, on average, 45.3 mmol CO(2) m(-2) night(-1) on a ground-area basis (or 334 mmol CO(2) kg(-1) night(-1) on a biomass basis) and 101 mmol CO(2) m(-2) night(-1) (or 361 mmol CO(2) kg(-1) night(-1)) at the drier site and the more mesic site, respectively. To model R(can) of Q. rubra (or other Quercus species with similar respiratory properties), variations in the base respiration rate across season, site and canopy position need to be fully accounted for, but E(0) may be assumed constant. Modeling R(can) at the mean nighttime temperature would not strongly affect estimated canopy carbon loss.