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Background: Plants can directly affect litter decomposition by producing litter materials of different qualities. However, whether living plants have indirect effects on litter decomposition by affecting changes in forest microenvironments is presently unclear in plantation forests. Methods: We addressed this issue by studying the decomposition of the leaf litter and fine roots of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.], a timber species widely planted in China, in 113 non-neighboring quadrats of varying basal area of the dominant plant species (i.e., Chinese fir) and distinct basal areas and species richness of regenerated woody plants (i.e., species other than Chinese fir) in a subtropical Chinese fir forest. Results: Our results showed that fine roots decomposed significantly more rapidly than leaf litter possibly because fine roots were easier access to mineralized nutrients and microbes compared with leaf litter. Further analyses showed that leaf litter and fine root decomposition rates were significantly controlled by the plant community attributes. The decomposition of both leaf litter and fine roots was mainly controlled by woody species regenerated during stand development rather than by Chinese fir. Specifically, leaf litter and fine root decomposition rates decreased with increasing basal area of regenerated woody plants, possibly due to nutrient competition and/or reduced photodegradation. Conclusions: This study provides empirical evidence that woody species regenerated during stand development play a certain role in determining litter decomposition rates through plant-soil interactions in Chinese fir plantations. Regenerated woody plants should be considered in future studies on soil carbon and nutrient cycling in plantation forest. [ABSTRACT FROM AUTHOR]

Soil acidification is an important cause of the productivity decline of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook)—one of the most important timber species in China. Although liming is an effective measure for reversing the effects of soil acidification, the effects on the morphologies and nutrients of different functional roots remain ambiguous. Thus, this study aimed to investigate the effects of liming on fine root traits of Chinese fir seedlings between two root function types (absorptive roots (AR) and transport roots (TR)). Chinese fir seedlings with equal performance were planted in each pot with two acidification soils (pH 3.6 and pH 4.3) and three levels of liming (0, 1000, and 4000 kg CaO ha−1). Our data showed that liming had no effect on the root biomass (RB) of AR and TR in mildly acidified soil, but it decreased the RB in severely acidified soil. Specific root length (SRL) of AR and TR were significantly increased by 24% and 27% with a high liming dose in mildly acidified soil, respectively. The specific root areas (SRA) of AR and TR were significantly increased by 10% and 22% with a high liming dose in mildly acidified soil, respectively. Furthermore, root N concentrations were significantly increased by 26% and 30% in AR and TR with a high liming dose in mildly acidified soil, respectively. Root P concentration of AR was significantly increased by 21% with a high liming dose in mildly acidified soil while root Ca concentration was significantly increased with all treatments. A similar trend was also observed in the Ca/Al ratio of roots. Both low and high doses of liming decreased the root Al concentration of AR by 26% and 31% in mildly acidified soil, respectively; however, there was no significant effect on TR in both soils. Our findings indicated that liming could alleviate Al toxicity to fine roots and increase root investment efficiency and absorption capacity. Liming also had coordinate effects on SRL, SRA, Root tissue density (RTD), N, P, Ca and Ca/Al between AR and TR. Our study suggested that to gain a comprehensive understanding of plant growth strategy, researchers in future studies must consider different functional roots rather than just the absorption part. Our results also revealed that the root system became more "acquisitive" due to the remediation of Al toxicity, which may be an important mechanism underlying the increment of the productivity of Chinese fir plantations undergoing liming. [ABSTRACT FROM AUTHOR]

Plant community may provide products and services to humans. However, patterns and drivers of community stability along a precipitation gradient remain unclear. A regional‐scale transect survey was conducted over a 3‐year period from 2013 to 2015, along a precipitation gradient from 275 to 555 mm and spanning 440 km in length from west to east in a temperate semiarid grassland of northern China, a central part of the Eurasian steppe. Our study provided regional‐scale evidence that the community stability increased with increasing precipitation in the semiarid ecosystem. The patterns of community stability along a precipitation gradient were ascribed to community composition and community dynamics, such as species richness and species asynchrony, rather than the abiotic effect of precipitation. Species richness regulated the temporal mean (μ) of aboveground net primary productivity (ANPP), while species asynchrony regulated the temporal standard deviation (σ) of ANPP, which in turn contributed to community stability. Our findings highlight the crucial role of community composition and community dynamics in regulating community stability under climate change. [ABSTRACT FROM AUTHOR]

Winter snowfall is an important water source for plants during summer in semiarid regions. Snow, rain, soil water, and plant water were sampled for hydrogen and oxygen stable isotopes analyses under control and increased snowfall conditions in the temperate steppe of Inner Mongolia, China. Our study showed that the snowfall contribution to plant water uptake continued throughout the growing season and was detectable even in the late growing season. Snowfall versus rainfall accounted for 30% and 70%, respectively, of the water source for plants, on the basis of hydrogen stable isotope signature (δD) analysis, and accounted for 12% and 88%, respectively, on the basis of oxygen stable isotope signature (δ18O) analysis. Water use partitioning between topsoil and subsoil was found among species with different rooting depths. Increased snowfall weakened complementarity of plant water use during summer. Our study provides insights into the relationships between precipitation regimes and species interactions in semiarid regions. [ABSTRACT FROM AUTHOR]

Purpose: Acid rain is a primary environmental problem in Southern China. However, the effect of acid rain on soil respiration rarely received attention, especially in ecosystems with different buffering capacities to acid rain. Thus, we explored how the response of soil respiration to simulated acid rain (SAR) in Cunninghamia lanceolata and Michelia macclurei plantations, which had great difference in the buffering capacities of their litter layers to acid rain.Materials and methods: The field experiment was subjected to a split-block experiment, with four main blocks in each plantation. Each block was split into A1 (SAR treatment, pH = 3) and A0 (deionized water, pH = 6.6) plots. Each plot was separated into subplots with (L0) and without (L1) litter treatments. SAR and deionized water were applied twice a month to A1 and A0 plots, respectively. From June 2016 to June 2017, soil respiration was measured twice per month using Li-8100 infrared gas analyzer. Soil temperature and moisture at a 5-cm depth were monitored using temperature and moisture sensors connected to Li-8100 during the measurement of soil respiration.Results and discussion: The result showed that SAR did not significantly influence soil respiration neither in C. lanceolate nor in M. macclurei plantations. However, the reasons for this result were probably different in the two plantations. The unchanged soil respiration in C. lanceolata plantation was mainly attributed to the negligible effect of SAR on fine root biomass and microbial biomass carbon (MBC) in C. lanceolata plantation because of the acclimation of fine root and microorganism to acid soil environment. In addition, the increase in fine root biomass and decrease in MBC may have resulted in the absence of the influence of SAR on soil respiration in M. macclurei plantation, because the variation of soil respiration derived from fine root under SAR may have offset that derived from microorganism.Conclusions: Although C. lanceolata and M. macclurei plantations had different buffering capacities to SAR, SAR did not significantly affect soil respiration in both plantations after 1 year of SAR treatment. Therefore, the long-term effect of SAR on soil respiration should be considered, particularly in forest types with different buffering capacities to acid rain. [ABSTRACT FROM AUTHOR]

Nitrogen addition has been shown to affect plant litter decomposition in terrestrial ecosystems. The way that nitrogen deposition impacts the relationship between plant litter decomposition and altered soil nitrogen availability is unclear, however. This study examined 18 co-occurring litter types in a subtropical forest in China in terms of their decomposition (1 yr of exposure in the field) with nitrogen addition treatment (0, 0.4, 1.6, and 4.0 mol·N·m−2·yr−1) and soil fauna exclusion (litter bags with 0.1 and 2 cm mesh size). Results showed that the plant litter decomposition rate is significantly reduced because of nitrogen addition; the strength of the nitrogen addition effect is closely related to the nitrogen addition levels. Plant litters with diverse quality responded to nitrogen addition differently. When soil fauna was present, the nitrogen addition effect on medium-quality or high-quality plant litter decomposition rate was −26% ± 5% and −29% ± 4%, respectively; these values are significantly higher than that of low-quality plant litter decomposition. The pattern is similar when soil fauna is absent. In general, the plant litter decomposition rate is decreased by soil fauna exclusion; an average inhibition of −17% ± 1.5% was exhibited across nitrogen addition treatment and litter quality groups. However, this effect is weakly related to nitrogen addition treatment and plant litter quality. We conclude that the variations in plant litter quality, nitrogen deposition, and soil fauna are important factors of decomposition and nutrient cycling in a subtropical forest ecosystem. [ABSTRACT FROM AUTHOR]

Background and aims: Freeze events can strongly influence many ecosystem processes. However, the effects of freeze events on litter production, litter quality, and decomposition are rarely documented. Methods: In this study, litter fall was measured monthly for 2 years. Two litter decomposition experiments were also performed using freeze-damaged litter and non-damaged litter in a loblolly pine forest. Results: The freeze event in November 2009 caused a pronounced pulse of needle litter fall. The freeze-damaged needle litter was shown to have higher N concentration and lower C/N ratio compared with the normal falling needle litter. This finding indicates that freeze damage significantly increased needle quality because of incomplete nutrient resorption. The decomposition of freeze-damaged needle litter was faster than that of normal falling yellow needle litter and slower than that of hand-picked green needle litter. The decomposition rate constant ( k) was negatively correlated with the C/N ratio in the needle litter. Our results also showed that the different climatic conditions influence patterns of litter decomposition. Conclusions: This study suggests that freeze events significantly alter litter quantity and quality, thus affecting litter decomposition rates in a loblolly pine forest in central China. [ABSTRACT FROM AUTHOR]

Masson pine (Pinus massoniana Lamb.), a native species widely distributed in temperate forests in central China, and Loblolly pine (Pinus taeda L.), an exotic tree species introduced to China from southeastern United States, are dominant evergreen conifers that play a pivotal role in maintaining forest structure and functions for the region. We examined the effects of freezing on these species with chlorophyll fluorescence and electrolyte leakage using both field- and laboratory-based experiments in September 2009 and January 2010, respectively. We found that freezing could cause a greater impact on the Loblolly pine than the Masson pine. Although the two species showed similar values of F v /F m and electrolyte leakage before freezing, the Masson pine needles showed lower F v /F m and higher electrolyte leakage ratios than those of the Loblolly pine when treated in low temperatures (−15 to 0°C). We also found that cold-acclimation was crucial for both species to adapt to low temperatures with the F v /F m ratio decreased approximately by 80% in the first freezing hour for the non-acclimated needles of both species while the cold-acclimated needles showed little changes in the F v /F m ratio. This finding is also supported by our measurements of electrolyte leakage. These results suggest that the Loblolly pine could be more susceptible to freezing damages than the Masson pine in central China. [ABSTRACT FROM AUTHOR]

Aims Although stem CO2 efflux is critical to ecosystem carbon and energy balance and its feedback to future climate change, little information is available on stem CO2 efflux and its responses to temperature, especially in subtropical China. This study aims to (i) evaluate the temporal and spatial variations of stem CO2 efflux of three species, including oak (Quercus acutissima Carr.), masson pine (Pinus massoniana Lamb.) and loblolly pine (Pinus taeda Linn.) in subtropical China and (ii) analyze the temperature sensitivity of stem CO2 efflux in the three species based on 2-year field measurements. Methods We measured stem CO2 efflux and stem temperature (at 3 cm depth) of the three species using the horizontally oriented soil chamber technique from September 2008 to August 2010. We also conducted a 24-h measurement to examine the diurnal variation of stem CO2 efflux in three consecutive days in April 2009. Important findings The temporal dynamics of stem CO2 efflux followed the change of the stem temperature in a 3-cm depth with a bell-shaped curve in the three species. Stem temperature explained 77–85% of the seasonal variations of stem CO2 efflux over the entire study period in the three species. The temperature sensitivity (Q10) of stem CO2 efflux was obviously different among the three species with higher Q10 value found in oak (2.24) and lower values in the coniferous species (1.76 and 1.63). Our results also showed that the Q10 values of stem CO2 efflux in all the three species were lower in the growing season than that in the non-growing season, indicating that the growth and maintenance respiration had different temperature responses. Moreover, we found that the temperature-normalized stem CO2 efflux (R10) changed greatly between the growing and non-growing seasons in oak and masson pine, but not in loblolly pine. Additionally, we also found that in the non-growing season, the principal factor responsible for the spatial variation of stem CO2 efflux among the 15 sampling trees was sapwood volume, whereas in the growing season, stem CO2 efflux was closely related to annual dry-matter production in the three subtropical species. [ABSTRACT FROM PUBLISHER]

Temperature sensitivity (Q10) of ecosystem respiration (ER) is a crucial parameter for predicting the fate of CO2 in terrestrial e cosystems under global warming. Most studies focus their attention in the variation of Q10 in one or two components of ER, but not in the integration or comparison among Q10 in major components of ER. Vertical and seasonal variations in individual components, including leaf respiration, stem respiration and soil respiration, of ER were observed synchronously along the gradient of leaf–stem–soil over a 2 year period in three forest stands dominated by masson pine, loblolly pine and oak, respectively, in a subtropical forest ecosystem of central China. We found that Q10 in individual components of ER increased along the vertical gradient of leaf–stem–soil. The vertical pattern of Q10 in individual components of ER was ascribed to variations of diurnal temperature range (DTR) and activation energy (ΔHa). These results suggest that a vertical pattern of Q10 in individual components of ER along the gradient of leaf–stem–soil should be taken into consideration in process-based models that simulate respiratory carbon flux in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Plant functional traits can serve as indicators of plant resource-use strategies in response to environmental changes. Plants growing in acidified soil exhibit conservative traits and limit growth, but there is still little known about changes in above- and belowground functional traits and their coordination under alleviation of soil acidification. Here, we conducted a pot experiment on raising soil pH by liming in Chinese fir (Cunninghamia lanceolata) saplings in southern China. The experiment involved in two degrees of acidified soil (Mild, pH = 4.3; Severe, pH = 3.6) and three liming treatments: Control (CK, 0), low liming treatment (L, 1000 kg CaO hm−2) and high liming treatment (H, 4000 kg CaO hm−2). We measured 22 above- and belowground functional traits of Chinese fir including allocation, morphological, photosynthetic, and chemical traits to assess their response to liming. The results show that liming enhanced aboveground mass fraction and total leaf area (TLA), and reduced construction cost (lower C concentration). However, specific leaf area (SLA), nutrient concentrations of N and P, and photosynthetic rate (Pn) remained unchanged. These results suggest that aboveground components exhibited acquisitive strategies in response to liming with greater TLA and lower construction cost. Moreover, liming reduced root mass fraction (RMF), increased specific root length (SRL), specific root area (SRA), and root N and Ca nutrient concentrations. These results suggest that belowground components also exhibited acquisitive strategies through constructing longer and thinner roots with greater metabolic rates. Our findings show that liming shifts above- and belowground resource-use strategies of Chinese fir from conservative to acquisitive. These changes in functional traits support the ability of Chinese fir to grow rapidly in response to alleviation of soil acidification. Our research not only contributes to a deeper understanding of plant adaptation mechanisms in the face of environment changes but also provides valuable insights for improving carbon sequestration of plantations in subtropical China. • 22 functional traits of Chinese fir were measured to assess their response to liming. • Liming elevated total leaf area and reduced leaf construction cost. • Liming elevated specific root length, specific root area and root N concentration. • Liming shifts resource-use strategies of Chinese fir towards acquisitive. [ABSTRACT FROM AUTHOR]

• Effect of wollastonite addition on SOC mineralization is evaluated. • Wollastonite addition increases SOC mineralization. • Greater wollastonite effect occurs on soils with lower pH values. • Soil trait change account for SOC mineralization response to wollastonite addition. Enhanced rock weathering through adding silicate rock powder to soil has been increasingly considered as an effective means of removing CO 2 from the atmosphere. However, the potential impact of silicate rock powder addition on the stability of soil organic carbon remains largely unknown, which adds an uncertainty to its effectiveness in mitigating atmospheric CO 2. In this study, the response of soil CO 2 efflux to wollastonite addition was evaluated for 12 land-use types in a subtropical region of China through an incubation experiment. Results showed that wollastonite addition significantly (P < 0.05) increased soil CO 2 efflux over the control by an average of 330.97 ± 29.25% during the incubation period. Approximately 90% of the variance in soil CO 2 efflux was explained by soil properties in this study. Increased soil pH, dissolved organic carbon and available silicon induced by wollastonite addition were the main reasons responsible for the increase in soil CO 2 emission. Soils having lower pH values responded to wollastonite addition with a higher increase in CO 2 emissions. Based on numerous land-use types, our study showed that wollastonite application will cause substantial increase in the mineralization of soil organic carbon in acidic soil, which may weaken the effectiveness of enhanced rock weathering strategies as a tool for CO 2 sequestration. [ABSTRACT FROM AUTHOR]

• Green leaf litter (GL) experienced a faster decay than senescence leaf litter (SL). • The temperature sensitivity (Q 10) of decomposition of GL was lower than that of SL. • The Q 10 of litter decomposition was negatively controlled by litter quality. • The faster litter decay after warm was due to reduced microbial carbon use efficiency. In the context of climate change, more frequent and severe extreme climate events are expected, which could lead to increased leaf fall before senescence. The decomposition of those abnormal fallen leaf litters may play a pivotal role in affecting the carbon (C) cycle in terrestrial ecosystems. Nevertheless, how their decomposition responds to temperature increase has rarely been studied, which limits the accurate estimation of the response of soil C dynamics to global warming and associated feedback. In the present study, green leaves (GL) were used to represent abnormal fallen leaf litters, and we compared the temperature sensitivity (Q 10) of the decomposition of GL with that of the corresponding senescent litters (SL) from nine species, which are widely distributed in subtropical China. Results showed that GL experienced a faster decomposition than SL. Conversely, the Q 10 of GL decomposition was significantly lower than that of SL decomposition. We also found that the Q 10 values of litter decomposition correlated positively with the C:N ratio and the lignin:N ratio, which supported the "C quality temperature" hypothesis. Furthermore, Q 10 was negatively controlled by phospholipid fatty acids of total microbes, fungi, and bacteria in soils. Experimental warming evidently increased the metabolic quotient of litter decomposition (q CO 2); a greater increase occurred in the decomposition of SL rather than that of GL. A positive correlation between Q 10 and warming-induced relative change in q CO 2 was also detected. We highlighted that the increasing inputs of abnormal fallen leaf litters caused by climate change could decrease the Q 10 of litter decomposition. [ABSTRACT FROM AUTHOR]

Background: Thermal acclimation of foliar respiration and photosynthesis is critical for projection of changes in carbon exchange of terrestrial ecosystems under global warming., Methodology/principal Findings: A field manipulative experiment was conducted to elevate foliar temperature (Tleaf) by 2.07°C in a temperate steppe in northern China. Rd/Tleaf curves (responses of dark respiration to Tleaf), An/Tleaf curves (responses of light-saturated net CO2 assimilation rates to Tleaf), responses of biochemical limitations and diffusion limitations in gross CO2 assimilation rates (Ag) to Tleaf, and foliar nitrogen (N) concentration in Stipa krylovii Roshev. were measured in 2010 (a dry year) and 2011 (a wet year). Significant thermal acclimation of Rd to 6-year experimental warming was found. However, An had a limited ability to acclimate to a warmer climate regime. Thermal acclimation of Rd was associated with not only the direct effects of warming, but also the changes in foliar N concentration induced by warming., Conclusions/significance: Warming decreased the temperature sensitivity (Q10) of the response of Rd/Ag ratio to Tleaf. Our findings may have important implications for improving ecosystem models in simulating carbon cycles and advancing understanding on the interactions between climate change and ecosystem functions.