Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

[Dissolved organic matter dynamics and spectral characteristics of twig litter from different Castanopsis carlesii forests in the middle subtropical region, China]. / ä¸­äºšçƒ­å¸¦ä¸åŒç±»åž‹ç±³æ§ æž—å‡‹è½æžæº¶è§£æ€§æœ‰æœºè´¨åŠ¨æ€åŠå ‰è°±å­¦ç‰¹æ€§.

To assess the dynamics and spectral characteristics of dissolved organic matter of twig litter in continuous increase stage, peak stage, and continuous decrease stage of twig litter production in different types of Castanopsis carlesii forest in middle subtropical China, a field experiment was conducted in C. carlesii natural forest, secondary forest and plantation. The results showed that litter production stage and forest type significantly affected the content and spectral characteristics of dissolved organic matter of twig litter were . Compared with the secondary forest and plantation, natural forest had higher dissolved organic carbon (DOC) content and lower special ultraviolet-visible absorption values at 254, 260 and 280 nm (SUVA254, SUVA260, SUVA280) at the continuous decrease stage of twig litter production, indicating high twig litter quality of natural forest and high cycling efficiency with dissolved organic matter in the natural forest at this stage. In contrast, the higher contents of total nitrogen (TN), total phosphorus (TP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and lower DOC:TDP and TDN:TDP ratios of twig litter in the plantation were observed at the peak stage of twig litter production, while no differences were detected in dissolved organic matter contents and spectral values in the secondary forest among the stages. In addition, the DOC, TDN, TDP of twig litter were negatively correlated with temperature and precipitation in the natural forests and secondary forests, but TDN and TDP of twig litter were positively correlated with temperature and precipitation in the plantations. These results suggested that the higher nutrient content at the peak stage of twig litter production in the C. carlesii plantation might lead to more efficient material cycling and that there would be a higher efficiency of material cycling for twig litter dissolved organic matter in C. carlesii natural forest at reduction stage of twig litter production.

[Nitrogen and phosphorus resorption and stoichiometric characteristics of different tree species in a mid-subtropical common-garden, China.] / ä¸­äºšçƒ­å¸¦åŒè´¨å›­ä¸åŒæ ‘ç§æ°®ç£·é‡å¸æ”¶åŠåŒ–å­¦è®¡é‡ç‰¹å¾.

To understand the nutrient use strategies of 11 tree species in a subtropical common-garden, we measured the specific leaf area, nitrogen (N) and phosphorus (P) resorption and stoichiometric characteristics of leaves in August 2019. The results showed that the specific leaf area, N and P concentrations in mature and senescent leaves of evergreen broadleaved (Lindera communis, Cinnamomum camphora, Schima superba, Castanopsis carlesii, Michelia macclurei and Elaeocarpus decipiens) and coniferous species (Cunninghamia lanceolata and Pinus massoniana) were lower than those of deciduous broadleaved species (Liquidambar formosana, Sapindus mukorossi and Liriodendron chinense). In contrast, C:N and C:P in mature leaves of evergreen broadleaved and coniferous species were significantly higher than those of deciduous broadleaved species. Except for C. carlesii, the N:P of all the species were lower than 14. Compared with other tree species, N and P resorption efficiencies of S. mukorossi were higher than 50% based on both mass and leaf area. Although P resorption efficiency of P. massoniana, C. lanceolata and C. camphora were higher than 50%, N and P resorption efficiency of M. macclurei were the lowest with only 15%-30%. In addition, specific leaf area of mature leaves was significantly positively correlated with N and P concentrations, but negatively correlated with C:N and C:P. In the common-garden, evergreen broadleaved species such as C. carlesii and L. communis, and coniferous species such as P. massoniana might belong to the slow investment species with lower specific leaf area, N and P concentrations, displaying relatively efficient in N and P resorption and utilization in comparison with other species. In contrast, deciduous broadleaved species such as S. mukoraiensis might be the fast investment species with low N and P use efficiency. Interestingly, tree species being restricted by N availability did not exhibit higher N resorption efficiency in the common-garden. Similarly, C. carlesii, the only P-restricted species here, did not exhibit higher P resorption efficiency. Our results provided scientific support for afforestation practice in the mid-subtropics.

[Effects of snow patches on the release of N and P during foliar litter decomposition in an alpine forest of western Sichuan China].

A field experiment using litterbags was conducted in an alpine forest of western Sichuan in order to understand the effects of snow patches on the dynamics of N and P during decomposition of six representative species foliar litter in different periods of winter. Net N immobilization during foliar litter decomposition was observed in the whole snow cover season regardless of species. In contrast, P mainly released from foliar litter in the snow cover season, with a rapid rate of P release in the snow melt stage. Thick and moderate snow patches showed higher P release rates, but lower N release rates of foliar litter. The rate of N release was negatively related to daily mean temperature regardless of species, but the rate of P release was positively related to daily mean temperature with the exception of fir needle-litter. The decrease of snow cover in the scenario of global warming could inhibit P release but promote N release from foliar litter decomposition in winter in the alpine forest.