Kerong Zhang

Effects of land use/land cover and climate changes on terrestrial net primary productivity in the Yangtze River Basin, China, from 2001 to 2010

Land use/land cover change (LULCC) and climate change are among the primary driving forces for terrestrial ecosystem productivity, but their impacts are confounded. The objective of this paper is to decouple the effects of LULCC and climate change on terrestrial net primary productivity (NPP) in Chinas Yangtze River Basin (YRB) during 2001–2010 using a light use efficiency model through different scenario designs. During the study period, the YRB witnessed tremendous LULCC and climate changes. A prominent LULCC was the conversion of shrub land to forests as a result of a series of forest restoration and protection programs implemented in the basin. At the same time, notable warming and drying trends were observed based on ground and satellite measurements. Prescribed model simulations indicated that LULCC alone had a significantly positive effect on total NPP (up to 6.1 Tg C yr−1, p < 0.01) mainly due to reforestation and forest protection, while climate change alone showed an overall negative effect in the basin (as much as −2.7 Tg C yr−1, p = 0.11). The ensemble effect of LULCC and climate change on total NPP is approximately 3.9 Tg C yr−1 (p = 0.26) during 2001–2010. Our study provides an improved understanding of the effects of LULCC and climate change on terrestrial ecosystem productivity in the YRB. We found that reforestation and forest protection could significantly enhance terrestrial ecosystem productivity, a strategy that could mitigate global warming. It also suggests that NPP models with static land use/land cover could lead to increasingly large errors with time.

Climate-growth relationships of subalpine fir (Abies fargesii) across the altitudinal range in the Shennongjia Mountains, central China

Dendroecological techniques were employed to explore the growth response of subalpine fir (Abies fargesii) to climatic conditions across its altitudinal range in both the north and south aspects in the Shennongjia Mountains, central China. Correlation function analyses indicated that temperatures in current summer were significantly negatively correlated with fir radial growth at the lower limits, while temperatures in previous autumn and in current spring showed significantly positive correlations with fir radial growth at the mid- and high-elevations in both aspects. Radial growth of the subalpine fir was significantly and positively influenced by precipitation in previous autumn and in current spring at the lower elevations and by precipitation in current spring at the mid-elevations, while precipitation had no significant effects on its radial growth at the upper elevations. Moving correlation functions showed that temperatures in early spring of the current year (i.e., February-April) had a relatively stable effect on tree growth over time at the mid- and upper-elevations in both aspects. Thus, the growth of the subalpine fir responded differently to climatic conditions along the altitudinal gradient, showing that the importance of temperatures for the fir radial growth increased while the importance of precipitation decreased with increasing altitude in both aspects in the Shennongjia Mountains, central China.

Response of soil physico-chemical properties to restoration approaches and submergence in the water level fluctuation zone of the Danjiangkou Reservoir, China

With the completion of the Danjiangkou Dam, the impoundment and drainage of dams can significantly alter shorelines, hydrological regime, and sediment and can result in the loss of soil and original riparian vegetation. Revegetation may affect soil properties and have broad important implications both for ecological services and soil recovery. In this work, we investigated the soil properties under different restoration approaches, and before and after submergence in the water level fluctuation zone (WLFZ) of the Danjiangkou Reservoir. Soil physical (bulk density and soil moisture), chemical (pH, soil organic carbon, nitrogen, phosphorus and potassium contents), and heavy metals were determined. This study reported that restoration approaches have impacts on soil moisture, pH, N, soil organic carbon, P, K and heavy metals in the WLFZ of the Danjiangkou Reservoir. Our results indicated that different restoration approaches could increase the soil moisture while decrease soil pH. Higher soil organic carbon in propagule banks transplantation (PBT) and shrubs restoration (SR) indicate that PBT and SR may provide soil organic matter more quickly than trees restoration (TR). SR and TR could significantly improve the soil total P and available P. PBT and SR could improve the soil total K and available K. SR and TR could significantly promote Cu and Zn adsorption, and Pb and Fe release by plant. Submergence could significantly affect the soil pH, NO3－-N, NH4＋-N, total P and available P. Submergence could promote NO3－-N and available P adsorption, and NH4＋-N and total P release by soil. The soil quality index (SQI) values implied that TR and PBT greatly improved soil quality. The present study suggests that PBT and TR could be effective for soil restoration in WLFZ of the Danjiangkou Reservoir.

Linking soil bacterial and fungal communities to vegetation succession following agricultural abandonment

Background and aimsGlobally, the rate and extent of cropland abandonment increase greatly since 1950s. Knowledge of soil bacteria and fungi succession during long-term vegetation development is particularly limited for the abandoned croplands. In order to test the effects of agricultural abandonment on soil biota succession, we studied the soil bacterial and fungal composition and diversity in abandoned farmlands across a century of secondary vegetation successional gradient in China’s Qinling Mountains.MethodsUsing high-throughput sequencing technologies, the soil fungal and bacterial communities were studied in 22 abandoned farmlands, as well as 7 adjacent arable fields representing non-abandoned references.ResultsThe stand age, i.e., years since agricultural abandonment, affected the soil bacterial and fungal composition and explained 8.7 and 31.6% variations of bacterial and fungal communities (at order level), repectively. The Proteobacteria, dominated by chemoorganotrophic bacteria, kept its absolute dominance status (38.66% - 40.77%) constantly during succession even though the vegetation changed obviously from crop to grass, shrub, and forest. The relative abundances of Acidobacteria, Planctomycetes, Verrucomicrobia, Nitrospirae, and Spirochaetes increased significantly with stand age (i.e., years since abandonment), while the Firmicutes, Actinobacteria, Gemmatimonadetes, Cyanobacteria, and Armatimonadetes showed an opposite trend. A distinct shift in fungal communities from Ascomycota -dominant in young stands to Basidiomycota -dominant in older stands was observed, which could be attributed to the increase of vegetation coverage and soil moisture during succession. The soil bacterial richness and diversity increased logarithmically with increasing stand age and gradually reached equilibrium in late-successional stage. Soil fungal diversity tended to increase in the early successional stages and then followed by a decreasing trend. The soil pH was the most important environmental factor predicating the soil fungal α-diversity measurements.ConclusionsBoth the soil bacterial and fungal communities displayed successional trends along with vegetation succession. The soil bacteria and fungi exhibited marked differences in successional pattern during secondary succession following agricultural abandonment.