RESUMO
The increases in frequency and intensity of drought worldwide has seriously affected tree growth, and even led to widespread forest mortality. Leaf traits estimated from pressure-volume (PV) curve provide key leaf physiological information that reflects the drought tolerance of trees. However, it is uncertain that which PV parameter performs the best at local scale. Here, we measured five PV traits (including TLP, π0, ε, Cleaf, and RWCtlp) and two leaf structural traits (specific leaf area and leaf density) in 20 tree species (16 angiosperms and 4 gymnosperms) in a temperate mixed forest at the Maoershan Forest Ecosystem Research Station, Northeast China. The objectives of this study were to search the best indicators of leaf drought tolerance at local scale, and to explore the correlation between PV traits and leaf structural traits. We found that angiosperms had significantly greater RWCtlp and lower Cleaf than gymnosperms, indicating that RWCtlp and Cleaf might be the good indicators of leaf drought tolerance in temperate mixed forest in Northeast China. Within angiosperm species, TLP and π0 were significantly and negatively correlated with leaf density, but positively correlated with specific leaf area; while ε was negatively correlated with specific leaf area. However, the opposite trends between PV traits and leaf structural traits were observed between gymnosperms and angiosperms, which might be attributed to their differences in drought response and adaptation strategies.
Assuntos
Secas , Árvores , China , Ecossistema , Florestas , Folhas de Planta/fisiologia , Árvores/fisiologia , Água/fisiologiaRESUMO
Thinning, an important forest management strategy, can alter forest structure and stability, and consequently affect ecosystem biogeochemical cycles. The effects of thinning on soil carbon and nitrogen is far from conclusive especially due to the lack of long-term experiments. Here, we investigated soil carbon and nitrogen in Larix olgensis plantations in Mengjiagang Forest Farm, Heilongjiang Province, with four thinning treatments (i.e., 4 times low-intensity thinning, LT4; 3 times medium-intensity thinning, MT3; 2 times high-intensity thinning, HT2; and un-thinned control). The effects of thinning on soil total organic carbon and total nitrogen were examined from the perspective of the composition of labile and recalcitrant pools (labile carbon or nitrogen pool I; labile carbon or nitrogen pool II; and recalcitrant carbon or nitrogen pool) by an acid hydrolysis approach. The results showed that thinning significantly increased soil total organic carbon and nitrogen by 48.7%-50.3% and 28.9%-42.7%, respectively. The carbon and nitrogen contents in all the labile I, labile II, and recalcitrant pools were increased by thinning, with the magnitudes varying across different pools and thinning types. LT4, MT3, and HT2 improved the recalcitrant carbon by 71%, 69% and 75%, respectively, which was significantly higher than the increment of two labile carbon pools. In addition, the percentage of recalcitrant carbon in total organic carbon was increased by thinning. LT4 significantly increased microbial biomass and microbial quotient, but no significant change was found in MT3 and HT2 treatments. Overall, our results indicated that thinning might increase the input of soil recalcitrant carbon components such as suberin and lignin by producing more coarse woody residues, thus leading to decline of organic matter decomposition and ultimately enhancement of soil organic carbon.
