The storage and utilization of carbohydrates in response to elevation mediated by tree organs in subtropical evergreen broad-leaved forests

Global climate change can affect tree growth and carbon sink function by influencing plant carbohydrate synthesis and utilization,while elevation can be used as an ideal setting under natural conditions to simulate climate change effects.The effect of elevation on tree growth may depend on organ type.However,the allocation patterns of nonstructural and structural carbohydrates(NSCs and SCs,respectively)in different tree organs and their response to elevation remain unclear.We selected four dominant tree species,Schima superba,Castanopsis eyrei,Castanopsis fargesii and Michelia maudiae,along an elevation gradient from 609 to 1,207 m in subtropical evergreen broad-leaved forests and analyzed leaf,trunk,and fine root NSCs,carbon(C),nitrogen(N)and phosphorus(P)concentrations and the relative abundance of SCs.Leaf NSCs increased initially and then decreased,and trunk NSCs increased with increasing elevation.However,root NSCs decreased with increasing elevation.The relative abundance of SCs in leaves and trunks decreased,while the relative abundance of root SCs increased with increasing elevation.No significant correlations between SCs and NSCs in leaves were detected,while there were negative correlations between SCs and NSCs in trunks,roots,and all organs.Hierarchical partitioning analysis indicated that plant C/N and C/P were the main predictors of changes in SCs and NSCs.Our results suggest that tree organs have divergent responses to elevation and that increasing elevation will inhibit the aboveground part growth and enhance the root growth of trees.A tradeoff between the C distribution used for growth and storage was confirmed along the elevation gradient,which is mainly manifested in the"sink"organs of NSCs.Our results provide insight into tree growth in the context of global climate change scenarios in subtropical forest ecosystems.

Temporal shifts in the explanatory power and relative importance of litter traits in regulating litter decomposition

Background:Litter traits critically affect litter decomposition from local to global scales.However,our understanding of the temporal dynamics of litter trait-decomposition linkages,especially their dependence on plant functional type remains limited.Methods:We decomposed the leaf litter of 203 tree species that belong to two different functional types(deciduous and evergreen)for 2 years in a subtropical forest in China.The Weibull residence model was used to describe the different stages of litter decomposition by calculating the time to 10%,25%and 50%mass loss(Weibull t_(1/10),t_(1/4),and t_(1/2)respectively)and litter mean residence time(Weibull MRT).The resulting model parameters were used to explore the control of litter traits(e.g.,N,P,condensed tannins and tensile strength)over leaf litter decomposition across different decomposition stages.Results:The litter traits we measured had lower explanatory power for the early stages(Weibull t_(1/10)and t_(1/4))than for the later stages(Weibull t_(1/2)and MRT)of decomposition.The relative importance of different types of litter traits in influencing decomposition changed dramatically during decomposition,with physical traits exerting predominant control for the stages of Weibull t_(1/10)and MRT and nutrient-related traits for the stages of Weibull t_(1/4),and t_(1/2).Moreover,we found that litter decomposition of the early three stages(Weibull t_(1/10),t_(1/4),and t_(1/2))of the two functional types was controlled by different types of litter traits;that is,the litter decomposition rates of deciduous species were predominately controlled by nutrient-related traits,while the litter decomposition rates of evergreen species were mainly controlled by carbon-related traits.Conclusions:This study suggests that litter trait-decomposition linkages vary with decomposition stages and are strongly mediated by plant functional type,highlighting the necessity to consider their temporal dynamics and plant functional types for improving predictions of litter decomposition.

Accumulation of residual soil microbial carbon in Chinese fir plantation soils after nitrogen and phosphorus additions

Nitrogen （N） and phosphorus （P） additions can affect soil microbial carbon （C） accumulation. However, the mechanisms that drive the changes in residual microbial C that occur after N and P additions have not been well-defined for Chinese fir plantations in subtropical China. We set up six different treatments, viz. a control （CK）, two N treatments （NI： 50kgha-1 a-1; N2： 100 kg ha-1 a-1）, one P treatment （P： 50 kg ha-1 a-1）, and two combined N and P treatments （NIP： 50kgha-1a-1 of N ＋50kgha-1a-1 of P; N2P：100 kg ha-1 a-1 of N ＋ 50 kg ha-1 a-1 of P）. We then investigated the influences of N and P additions on residual microbial C. The results showed that soil pH and microbial biomass decreased after N additions, while microbial biomass increased after P additions. Soil organic carbon （SOC） and residual microbial C contents increased in the N and P treatments but not in the control. Residual microbial C accumulation varied according to treatment and declined in the order： N2P 〉 N1P 〉 N2 〉 N1 〉 P 〉 CK. Residual microbial C contents were positively correlated with available N, P, and SOC contents, but were negatively correlated with soil pH. The ratio of residual fungal C to residual bacterial C increased under P additions, but declined under combined N1P additions. The ratio of residual microbial C to SOC increased from 11 to 14% under the N1P and N2P treatments, respectively. Our results suggest that the concentrations of residual microbial C and the stability of SOC would increase under combined applications of N and P fertilizers in subtropical Chinese fir plantation soils.

Climate change impacts flowering phenology in Gongga Mountains,Southwest China

Flowering phenology of plants,which is important for reproductive growth,has been shown to be influenced by climate change.Understanding how flowering phenology responds to climate change and exploring the variation of this response across plant groups can help predict structural and functional changes in plant communities in response to ongoing climate change.Here,we used long-term collections of 33 flowering plant species from the Gongga Mountains(Mt.Gongga hereafter),a biodiversity hotspot,to investigate how plant flowering phenology changed over the past 70 years in response to climate change.We found that mean flowering times in Mt.Gongga were delayed in all vegetation types and elevations over the last 70 years.Furthermore,flowering time was delayed more in lowlands than at high elevations.Interestingly,we observed that spring-flowering plants show earlier flowering times whereas summer/autumn plants show delayed flowering times.Non-synchronous flowering phenology across species was mainly driven by changes in temperature and precipitation.We also found that the flowering phenology of 78.8%plant species was delayed in response to warming temperatures.Our findings also indicate that the magnitude and direction of variation in plant flowering times vary significantly among species along elevation gradients.Shifts in flowering time might cause trophic mismatches with co-occurring and related species,affecting both forest ecosystem structure and function.

Litter age interacted with N and P addition to impact soil N_(2)O emissions in Cunninghamia lanceolata plantations

Litter decomposition impacts carbon(C)and nutrient cycling.Nitrogen(N)and phosphorus(P)addition as well as litter age impact litter decomposition.Effects of nutrient addition and litter age on litter decomposition may impact emissions of soil nitrous oxide(N_(2)O),which is an important greenhouse gas.However,no study has examined the effects of interactions between litter age and nutrient addition on soil N_(2)O emissions,and explored the underlining mechanisms simultaneously,thus limiting our evaluation of litter decomposition effects on N_(2)O emissions.Litter with different age was collected from Cunninghamia lanceolata plantations experienced N and P addition treatments to examine the effects of nutrient addition and litter age on N_(2)O emissions by incubation study.Litter age generally increased N_(2)O emissions via a decrease in litter C:N ratio.While P addition decreased N_(2)O emissions,N addition increased them mainly by positive effects on soil enzymes as indicated by microbial functional genes associated with N_(2)O production and negative effects on litter C:N ratio.Litter age and nutrient addition interacted to impact soil N_(2)O emissions.In future forest management,both nutrient addition and litter age should be considered in evaluation of management effects on N_(2)O emissions,especially thinning or selectively cutting involving litter input with different age.