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Plants allocate a substantial amount of C belowground for root exudates and for the construction and adjustment of root morphological and architectural traits. What relationships exist between root exudates and other root traits and these relationships change with growing season, however, remain unclear. We quantified the root exudation rate and root morphological traits, including total root length (RL), total root surface area (RS), root diameter (RD), specific root length (SRL), specific root area (SRA) and root tissue density (RTD), and architectural traits, such as branching intensity (BI), and investigated their associations during the rapidly growing season (April and August) and the slowly growing season (December) of three common native tree species, Liquidambar formosana , Michelia maudiae and Schima superba , in subtropical China. We found that the linkages of RD, SRL, SRA, RTD and BI did not change with the growing season, reflecting their highly conservative relationships. The root exudation rate varied significantly with growing season (P  < 0.05) and produced various associations with other root traits at different growing seasons. During the rapidly growing season (i.e. April), the exudation rate was the highest and was positively correlated with RL. The exudation rate was the lowest during the slowly growing season (i.e. December) and was negatively associated with RL, RS and RTD. Our findings demonstrate the seasonality of the linkages of root exudation rate with other root traits, which highlights the highly plastic and complex associations of belowground root traits. These findings help to deepen our understanding of plant nutrient acquisition strategies. [ABSTRACT FROM AUTHOR]

Plants allocate nutrients to new leaves via making a cost–benefit trade‐off between root nutrient absorption ('get') and leaf nutrient resorption ('save'). This active trade‐off in nutrient acquisition pathways may cause a passive trade‐off between resorption and decomposition ('return'). However, whether these nutrient‐associated processes are linked and form a 'get‐save‐return' (GSR) continuum, and its linkages with the above‐ground leaf economics spectrum (LES) and the below‐ground mycorrhizal association remain unclear.Here, we present the first empirical evidence of a direct link among multiple nutrient‐associated processes and tested this continuum hypothesis by synchronously integrating root nutrient absorption, leaf nutrient resorption and leaf litter decomposition of 15 co‐occurring tree species hosting either arbuscular mycorrhizal or ectomycorrhizal fungi in subtropical forests of China.Across species, there was an active trade‐off between phosphorus (P) absorption and resorption, which further caused a passive trade‐off between P resorption and leaf litter decomposition, indicating that the GSR continuum exists and runs on P economy. However, these processes associated with nitrogen economy were not well linked. Interestingly, the loading scores of species on the LES were positively correlated with root P absorption, negatively with leaf P resorption and positively with leaf litter decomposition. These linkages indicate that species running in the 'fast lane' had greater root P absorption, lower leaf P resorption and faster leaf litter decomposition than species running in the 'slow lane', and that the process‐based GSR continuum follows the trait‐based 'fast‐slow' LES. Furthermore, the continuum on P economy emerged evidently in the ectomycorrhizal tree species rather than in the arbuscular mycorrhizal tree species, indicating critical control of mycorrhizal association over the continuum.Synthesis. Overall, these results demonstrate the existence of the GSR continuum on tree P economy, which conforms to the economics spectrum theory but varies with mycorrhizal association type. Our findings provide a process‐based framework for mechanistic understanding of the whole plant nutrient economy and ecosystem nutrient cycling, and facilitate improved predictions of biogeochemical models. [ABSTRACT FROM AUTHOR]

After decades of afforestation, China's forest coverage has increased significantly, but the forest quality and its impact on ecosystem services are still controversial. Taking forest vegetation carbon storage as an example, most assessment results based on the national forest inventory data showed that the contribution of enlarged forest area to the increase in China's forest vegetation carbon storage was higher than that of the change in forest quality (vegetation carbon density). This means that the increase in forest carbon storage in China was mostly contributed by the increase in forest area and was less due to the increased forest vegetation carbon density. However, the national forest inventory data are based on national permanent plots that may be protected or are less disturbed to some extent. Therefore, the contribution of the change in forest quality to the increase in forest vegetation carbon storage, as evaluated from the national forest inventory data, might be overestimated, especially in regions with frequent human activities. To test the hypothesis, we selected Taihe County, a typical representative of the red soil hilly region in subtropical China, where the population is dense, economic development is fast, and the forest has experienced destruction and re-establishment. To accurately assess the impact of changes in the forest area and forest quality on forest vegetation carbon storage variation in real situations, we collected and used a series of remote sensing images from 1986 to 2019, inventory data for forest management, and field data. The results showed that the forest area and forest vegetation carbon density increased from 10.85 × 104 ha and 17.89 Mg/ha in 1986 to 16.40 × 104 ha and 26.51 Mg/ha in 2019, with an increase of 51.11% and 48.23%, respectively. Meanwhile, the forest vegetation carbon storage increased by 123.99%, from 1.94 Tg in 1986 to 4.35 Tg in 2019, suggesting a significant carbon sequestration ability. Further analysis showed that the contributions of changes in forest area and forest quality to the forest vegetation carbon storage variation were 1.23 Tg (51.19%) and 1.17 Tg (48.81%), respectively. The result implies that the increase in forest area and forest quality almost contributed equally to the increase in forest vegetation carbon storage during the 34 years of vegetation restoration in Taihe County. However, forest vegetation carbon density controlled the variation of forest vegetation carbon storage in all three forest developing stages. The precision of our results was also tested with two inventory datasets for forest management in Taihe County in 2009 and 2019. The relative contribution of forest vegetation carbon density is lower than most of the previous study results using national forest inventory data in this region, indicating that the contribution of change in the forest vegetation carbon density to the forest vegetation carbon storage variation might be overestimated based on these national permanent plots, which were protected or less disturbed to some extent. [ABSTRACT FROM AUTHOR]

Decomposition is vital for nutrient cycling and is sensitive to atmospheric nutrient depositions. However, the influences and underlying mechanisms of nutrient deposition on the long-term decomposition of leaves and absorptive roots remain unclear. Here, we explored the responses of leaves and absorptive roots to nutrient deposition (control, +N, +P, and +NP) in Pinus massoniana and Schima superba forests in subtropical China based on two stages (early-stage (1-year) and late-stage (3-year)) of a decomposition experiment. The chemical factions (acid-unhydrolysable residue (AUR), cellulose, and hemicellulose concentrations) and microbial enzymatic activities (hydrolase and oxidase) were also determined. The +N treatment had persistent negative effects on absorptive root decomposition, except for P. massoniana during the late stage. The +P treatment had a positive effect on leaf decomposition in all stages. The +NP treatment had a positive effect on leaf decomposition during the late stage. The increasing decomposition rates of foliar under +P treatment were more correlated with the increasing acid phosphatase activity than chemical factions, indicating a microbial mechanism. The decreasing decomposition rates of roots under +N treatment were weakly correlated with increasing AUR concentrations and strongly correlated with decreasing oxidase activity during the late stage, indicating both chemical and microbial mechanisms. Overall, our findings highlight that, despite contrasting responses to nutrient deposition, the mechanisms underlying aboveground and belowground decomposition tend to converge as decomposition progresses. [ABSTRACT FROM AUTHOR]

Summary: The root economics space (RES) is multidimensional and largely shaped by belowground biotic and abiotic influences. However, how root–fungal symbioses and edaphic fertility drive this complexity remains unclear.Here, we measured absorptive root traits of 112 tree species in temperate and subtropical forests of China, including traits linked to functional differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) hosts.Our data, from known mycorrhizal tree species, revealed a 'fungal‐symbiosis' dimension distinguishing AM from ECM species. This divergence likely resulted from the contrasting mycorrhizal evolutionary development of AM vs ECM associations. Increased root tissue cortical space facilitates AM symbiosis, whereas increased root branching favours ECM symbiosis. Irrespective of mycorrhizal type, a 'root‐lifespan' dimension reflecting aspects of root construction cost and defence was controlled by variation in specific root length and root tissue density, which was fully independent of root nitrogen content. Within this function‐based RES, we observed a substantial covariation of axes with soil phosphorus and nitrate levels, highlighting the role played by these two axes in nutrient acquisition and conservation.Overall, our findings demonstrate the importance of evolved mycorrhizal symbiosis pathway and edaphic fertility in framing the RES, and provide theoretical and mechanistic insights into the complexity of root economics. [ABSTRACT FROM AUTHOR]

Aims: Multi-elemental stoichiometry can represent the biogeochemical niches of species, which can further guide community assemblage. Mycorrhizae play a key role in plant elemental acquisition. Whether and how mycorrhizal type influences the plant multi-elemental stoichiometries and elemental coordination in above- and belowground organs, however, remain unclear. Methods: We determined the concentrations of C, N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, Na, Pb and Sr and some elemental ratios in the leaves and roots of arbuscular mycorrhizal (AM) trees (Phoebe bournei, Schima superba, Michelia maudiae and Cunninghamia lanceolata) and ectomycorrhizal (ECM) trees (Cyclobalanopsis glauca, Pinus massoniana and P. elliottii) in subtropical China. The effects of root traits and soil abiotic factors on elemental concentrations and ratios were reported. Results: The elemental concentrations and ratios differed substantially between the AM and ECM trees, indicating the their biogeochemical niches' differentiation. The C, P, Mg and Mn concentrations and the K:Mg andCa:Mg ratios for AM and the N, Mn and Na concentrations and the Fe:Mn ratio for the ECM species were strongly correlated between leaves and roots, but the correlations were positive or negative depending on elemental composition and mycorrhizal type. The root branching ratio, branching intensity and length played important roles in the plant elemental stoichiometries. Conclusions: The biogeochemical niche's differentiation between the AM and ECM species emphasizes the important role of mycorrhizal type in the assemblage of co-occurring species. This study offers a new opinion for species choosing in mixed forests from the view of the biogeochemical niche's separation. [ABSTRACT FROM AUTHOR]

Summary: Traits are critical in predicting decomposition that fuels carbon and nutrient cycling in ecosystems. However, our understanding of root trait–decomposition linkage, and especially its dependence on mycorrhizal type and environmental context, remains limited.We explored the control of morphological and chemical (carbon‐ and nutrient‐related) traits over decomposition of absorptive roots in 30 tree species associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi in temperate and subtropical forests in China.Carbon‐related traits (acid‐unhydrolysable residue (AUR) and cellulose concentrations) had predominant control of root decomposition in AM species while nutrient‐related traits (magnesium concentration) predominately controlled that in ECM species. Thicker absorptive roots decomposed faster in AM species as a result of their lower AUR concentrations, but more slowly in ECM angiosperm species potentially as a result of their higher magnesium concentrations. Root decomposition was linked to root nutrient economy in both forests while root diameter–decomposition coordination emerged only in the subtropical forest where root diameter and decomposition presented similar cross‐species variations.Our findings suggest that root trait–decomposition linkages differ strongly with mycorrhizal type and environment, and that root diameter can predict decomposition but in opposing directions and with contrasting mechanisms for AM and ECM species. [ABSTRACT FROM AUTHOR]

• Annual CH 4 emissions from rice paddy were evaluated with 7-yearlong dataset. • Daily CH 4 flux and GPP showed a logarithmic relation at vegetative stage. • No significant association was found between annual CH 4 emission and GPP. • Soil temperature was the dominant driver affecting the interannual CH 4 emission. Rice paddies are important sources of the greenhouse gas methane (CH 4). However, it is difficult to precisely quantify CH 4 emissions using the static chamber method because of their discontinuous measurements as well as the spatial and temporal variability of CH 4 emissions. To precisely quantify CH 4 emissions from rice paddies and gain deep insight into the emission rhythm and environmental effects, a seven-yearlong CH 4 flux measurement was carried out continuously using the eddy covariance method in a double cropping rice paddy in subtropical China. The annual CH 4 emissions were 42 ± 2 g C m−2. The half hourly CH 4 flux was highly correlated with gross primary production (GPP) and environmental factors, such as soil temperature (Ts), and latent heat flux (LE), which explain 47–91% of the CH 4 diurnal variation. However, the peak of CH 4 generally appeared at dusk during the vigorous growth period, which was quite different from the GPP peak around noon. CH 4 flux seasonal dynamic were more complex, with double peaks during the growing season and lower values during the fallow season. Interestingly, in contrast to previous studies of linear or exponential relationships with short-term datasets, daily CH 4 and GPP showed a logarithmic relationship at the vegetative stage in this study with seven-year data, this is crucial in improving the model accuracy in estimating annual CH 4 emissions. The result implies that long-term observation is necessary to accurately assess CH 4 emissions from rice paddy. [ABSTRACT FROM AUTHOR]

Compared with CO2, methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases in terms of their global warming potentials. Previous studies have indicated that land-use conversion has a significant impact on greenhouse gas emissions. However, little is known regarding the impact of converting rice (Oryza sativa L.) to vegetable fields, an increasing trend in land-use change in southern China, on CH4 and N2O fluxes. The effects of converting double rice cropping to vegetables on CH4 and N2O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH4 fluxes could reach 31.6 mg C m−2 h−1 under rice before land conversion. The cumulative CH4 emissions for fertilized and unfertilized rice were 348.9 and 321.0 kg C ha−1 yr−1, respectively. After the land conversion, the cumulative CH4 emissions were −0.4 and 1.4 kg C ha−1 yr−1 for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N2O fluxes under rice were 1.27 and 0.56 kg N ha−1 yr−1 for the fertilized and unfertilized treatments before the land conversion and 19.2 and 8.5 kg N ha−1 yr−1, respectively, after the land conversion. By combining the global warming potentials (GWPs) of both gases, the overall land-use conversion effect was minor (P = 0.36) with fertilization, but the conversion reduced GWP by 63% when rice and vegetables were not fertilized. Increase in CH4 emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N2O emissions compensated for similar GWPs with fertilization under rice and vegetables. [ABSTRACT FROM AUTHOR]

Because evapotranspiration (ET) is the second largest component of the water cycle and a critical process in terrestrial ecosystems, understanding the inter-annual variability of ET is important in the context of global climate change. Eight years of continuous eddy covariance measurements (2003–2010) in a subtropical coniferous plantation were used to investigate the impacts of climatic factors and ecosystem responses on the inter-annual variability of ET. The mean and standard deviation of annual ET for 2003–2010 were 786.9 and 103.4 mm (with a coefficient of variation of 13.1%), respectively. The inter-annual variability of ET was largely created in three periods: March, May–June, and October, which are the transition periods between seasons. A set of look-up table approaches were used to separate the sources of inter-annual variability of ET. The annual ETs were calculated by assuming that (a) both the climate and ecosystem responses among years are variable (Vcli-eco), (b) the climate is variable but the ecosystem responses are constant (Vcli), and (c) the climate is constant but ecosystem responses are variable (Veco). The ETs that were calculated under the above assumptions suggested that the inter-annual variability of ET was dominated by ecosystem responses and that there was a negative interaction between the effects of climate and ecosystem responses. These results suggested that for long-term predictions of water and energy balance in global climate change projections, the ecosystem responses must be taken into account to better constrain the uncertainties associated with estimation. [ABSTRACT FROM AUTHOR]

Highlights: [•] We analyzed change trends of the climate variables ET 0 and AI in an arid region of China over the past 50years. [•] We identified the sensitivity of ET 0 and AI to the main climate variables. [•] We quantified the contributions of climate variables to the changes in ET 0 and AI. [•] Contribution of wind speed decline to decrease of ET 0 is larger than other climate variables. [•] The increase of precipitation contributes more than the decrease of ET 0 to decrease of AI. [ABSTRACT FROM AUTHOR]

This article outlines the human activities and its impact on water-land environment in the Minqin oasis of northwest China which is an area of typical arid features. During the last century, human activities have caused a series of detrimental water-land environment responses. Analyses show that runoff into the Minqin oasis has been reduced, with the decreasing trend predominantly occurring during the periods of July to September and December to February, perpetrated by construction of reservoirs and diversion of runoff for irrigation in the upper and middle reaches of the Shiyang River basin. In addition, excessive quantities of groundwater in the Minqin oasis have been exploited, producing serious groundwater level declines. Groundwater quality has also degenerated, with total dissolved solids (TDS) concentrations in the northern portion of the oasis reaching 5.76 g l-1. The continual lowering of the groundwater surface and increased groundwater quality degradation has produced negative changes in the ecological environment. The area of salinized soil has doubled from the 1950s to the present value of 4000 ha, with vegetation cover in the Minqin oasis seriously degenerated, marred by land desertification and frequent dust storms. Strategies for improving the water-land environment of the oasis are proposed in this article, with guidelines for reconstruction of sustainable water-land management in Minqin oasis. [ABSTRACT FROM AUTHOR]

Unique soil properties in rhizosphere can affect plant growth and biogeochemical cycles of ecosystems. While rhizosphere has been widely investigated, little is known about differences in the rhizosphere effect (RE) between co-existing overstory trees and understory shrubs and herbs in forest ecosystems. In this study, we investigated REs on soil chemical properties of overstory trees and understory shrubs and herbs in forest plantations of southern China. Bulk soil and rhizospheres were sampled in April, July and December 2017. Soil pH, nitrate and ammonium nitrogen, dissolved organic carbon, available phosphorus, total carbon, total nitrogen, and total phosphorus were tested. The REs were defined as the ratios of the chemical properties of the rhizospheres to those of the bulk soil. Our results showed that pH was lower and nutrient contents were higher in the plant rhizospheres than the bulk soil. REs were generally larger in trees than understory plants. The REs were larger in July than April and December. Our findings indicated that the RE varied among plant life forms, species and sampling times, emphasizing the functional role of the RE of understory vegetation in subtropical forests. • Rhizospheres had lower pH and higher nutrient contents than bulk soil. • Trees had higher rhizosphere effects than understory shrubs and herbs. • The rhizosphere effects were higher in active growing season. [ABSTRACT FROM AUTHOR]

Abstract: Forest soils are important sources for nitrous oxide (N2O), but how the surface litter layer affects these sources is still unclear. Seasonal rainfall in the subtropical monsoon climate provides a unique opportunity to examine soil–atmosphere N2O flux under a wide range of soil water content. We studied this question over 3 years using a litter removal method in a 20-year-old pine plantation (Pinus elliottii) in subtropical China. Annual mean chamber-based soil–atmosphere N2O fluxes of the control (F CK) and litter-free (F LF) treatments were 6.07 and 5.17 μg N2O m−2 h−1, respectively. Removal of the litter layer reduced 15% of soil N2O emissions, suggesting the mineral soil as the dominant factor that determines soil N2O emissions. Seasonal F CK and F LF were both significantly influenced by water-filled pore space (WFPS) but not by soil temperature (T S). However, F CK and F LF were both correlated with T S during the wet season (January–June) but not during the dry season (July–December). During the wet season, F CK and F LF were 84% and 132% higher than during the dry season, respectively. In contrast, seasonal litter-based N2O fluxes (F CK−LF = F CK − F LF) were not correlated with WFPS and T S. During the dry season, however, a positive relationship was observed for F CK−LF and WFPS. In the context of climate change and human activities, future changes in soil environment and surface litter management will alter the strength of soil N2O emissions of the subtropical pine forests in China. [Copyright &y& Elsevier]

• C:N:P ratios differed significantly among species. • Forest type significantly influenced C:N:P ratios of leaves and rhizosphere soils. • Foliar and root C:N:P ratios were constrained by rhizosphere. Ecological stoichiometry provides important information for understanding biogeochemical cycling in forest ecosystems. The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in the leaves, roots and rhizosphere soils of co-existing overstory trees and understory shrubs and herbs within a forest ecosystem, however, remain poorly understood. The C, N and P concentrations and their stoichiometric ratios of the leaves, roots and rhizosphere soils were studied for three overstory trees, three understory shrubs and two herbs in three plantations of Cunninghamia lanceolata , Pinus massoniana and Pinus elliottii in subtropical China. Mostly, the foliar and root C:N ratios were significantly higher for overstory trees than understory shrubs and herbs. Forest type significantly influenced the C:N and C:P ratios of the leaves and rhizosphere soils across all species. The C:N ratio in the leaves and roots were positively and negatively correlated with that in rhizosphere soil, respectively. The N:P in leaves and roots were negatively and positively correlated with that of rhizosphere soil, respectively. We found that foliar and root C:N:P stoichiometry varied greatly among plant species and forest types, which was mainly constrained by the rhizosphere soil. The opposite relationship of C:N:P stoichiometry in the leaves and roots with rhizosphere soil offers new insights into the interaction between above- and belowground process of forest ecosystems. [ABSTRACT FROM AUTHOR]