Abandoned Land Research Articles

Differential soil microbial community responses to the linkage of soil organic carbon fractions with respiration across land-use changes

Abstract Land-use change can modify terrestrial ecosystem processes with potentially important effects on below-ground carbon dynamics. Soil microbes are considered the rate-limiting factor in carbon decomposition. However, the effect of land-use change on soil microbial community and the mechanism of soil carbon dynamics remain unclear. In this study, soil samples were collected during four periods (April, June, August, and October) at sites in the Loess Plateau in China with different land- use types: Robinia pseudoacacia L. (RP) and abandoned land (AL); these areas were converted 40 years ago from similar farmlands, while the millet (Setaria italica) farmlands (FL) were selected as a control in our study. Quantitative PCR and Illumina sequencing of the 16S rRNA and ITS genes were performed to analyze the abundance, diversity, and compositions of the soil microbes (bacteria and fungi). Additionally, soil organic carbon fractions (soil organic carbon: SOC, dissolved organic carbon: DOC, microbial biomass carbon: MBC) and soil respiration components (soil respiration: SR, heterotrophic respiration: HR, autotrophic respiration: AR) were evaluated. The results showed that SOC fractions and soil respiration increased after land-use change, with significant correlation being observed. In particular, DOC was more related to SR and HR than to the other fractions. Moreover, the abundance and diversity of the microbes (bacteria and fungi) were greatly affected by the land- use change; both of them were significantly and positively correlated with soil organic carbon fractions and soil respiration components. For dominant bacterial phyla, both Proteobacteria and Bacteroidetes were significantly more abundant in the afforested soil than in the FL, while the abundances of Actinobacteria and Chloroflexi ranked as FL > AL > RP. For dominant fungal phyla, Ascomycota responded positively to land- use changes, whereas Basidiomycota responded negatively. Such changes in the abundances of microbial phyla were significantly correlated with the linkage of soil organic carbon fractions and respiration components. Altogether, these results suggest that the changes in components of soil respiration may be highly susceptible to soil organic carbon fractions, especially to DOC, and this linkage is largely modulated by microbial community across land-use changes.

Response of microbial diversity to C:N:P stoichiometry in fine root and microbial biomass following afforestation

Soil samples were collected in June and October from areas with three land-use types, i.e., Robinia pseudoacacia L. (RP), Caragana korshinskii Kom. (CK), and abandoned land (AL), of which the former two were afforested areas, whereas the latter was not. These areas were converted from similar farmlands 40 years prior. Illumina sequencing of 16S rRNA gene and fungal ITS gene was used to analyze soil bacterial and fungal diversity. Additionally, plant communities, soil properties, fine root biomass, and C, N, and P levels in fine root and microbial biomass were estimated. Compared to AL, the C:N:P stoichiometry in fine root and microbial biomass in the afforested lands was synchronously changed, especially the N:P ratio. Soil microbial diversities were affected by afforestation and were more related to N:P ratio than C:P and C:N ratios. Moreover, Alpha-proteobacteria, Gamma-proteobacteria, and Bacteroidetes were significantly more abundant in afforested soils than in the AL soil, and the abundances of Actinobacteria, Chloroflexi, Cyanobacteria, and Nitrospirae ranked as AL > RP or CK. For fungal taxa, Ascomycota abundance responded positively to afforestation, whereas Basidiomycota abundance responded negatively. Changes of soil microbial taxa were significantly correlated with the N:P ratio in fine root and microbial biomass, which explained 54.1 and 55% of the total variation in bacterial and fungal taxa, respectively. Thus, our results provide evidence that compositions of soil microbial communities are linked to the N:P ratio in the plant-soil system.

Responsiveness of soil nitrogen fractions and bacterial communities to afforestation in the Loess Hilly Region (LHR) of China.

In the present paper, we investigated the effects of afforestation on nitrogen fractions and microbial communities. A total of 24 soil samples were collected from farmland (FL) and three afforested lands, namely Robinia pseudoacacia L (RP), Caragana korshinskii Kom (CK), and abandoned land (AL), which have been arable for the past 40 years. Quantitative PCR and Illumina sequencing of 16S rRNA genes were used to analyze soil bacterial abundance, diversity, and composition. Additionally, soil nitrogen (N) stocks and fractions were estimated. The results showed that soil N stock, N fractions, and bacterial abundance and diversity increased following afforestation. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla of soil bacterial compositions. Overall, soil bacterial compositions generally changed from Actinobacteria (Acidobacteria)-dominant to Proteobacteria-dominant following afforestation. Soil N fractions, especially for dissolved organic nitrogen (DON), were significantly correlated with most bacterial groups and bacterial diversity, while potential competitive interactions between Proteobacteria (order Rhizobiales) and Cyanobacteria were suggested. In contrast, nitrate nitrogen (NO3−-N) influenced soil bacterial compositions less than other N fractions. Therefore, the present study demonstrated that bacterial diversity and specific species respond to farmland-to-forest conversion and hence have the potential to affect N dynamic processes in the Loess Plateau.

Changes of soil organic carbon, nitrogen and phosphorus concentrations under different land uses in marshes of Sanjiang Plain

Wetlands provide a large pool of organic matter and nutrients, and are important for maintaining material cycle balances in terrestrial ecosystems, and also help retard climate change. Land use changes in wetlands have greatly disturbed the natural evolution of wetland ecosystems. Wetland drainage and reclamation alters the physical, chemical and biological conditions of the wetland, thus significantly disturbing the material cycles, leading to significant changes in the biogeochemical processes of carbon, nitrogen and phosphorus in the wetland. The wetlands in the Sanjiang Plain are the largest area of fresh wetlands in China. However, the area has experienced major land uses changes since the 1950s; areas of the wetland have been drained and converted to arable land. Some studies have been conducted into the effects of land use change on material cycles in the Sanjiang Plain wetlands but few reports have discussed the C/N and C/P ratios and pH values as indicators of wetland degradation due to land use changes. We selected eight land uses: humus marsh (HM), marshy meadow (MM), drained humus marsh (DHM), drained marshy meadow (DMM), tillage land (TL), abandoned land (AL), natural secondary forest (NSF) and artificial forest (AF), in the Honghe area of the Sanjiang Plain. We studied changes in the total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), C/N and C/P ratios and pH values in topsoil (0–20cm) of these eight different land uses. The possible mechanisms underlying the changes, and the significance of the C/N and C/P ratios as indicators of soil quality were also discussed. In the natural wetland, the TOC, TN and TP concentrations in the soil were high, with values of 203.5g/kg, 20.2g/kg and 1.44g/kg, respectively, in HM; and 59.2g/kg, 5.28g/kg and 0.83g/kg, respectively, in MM. Drainage of the HM has led to decreases in the TOC, TN and TP concentrations of about 50%. Significant decreases were also observed in TOC, TN and TP for NSF and AF compared to HM. Drained MM led to decreases in the TOC and TN of about 45%, but had little effect on TP. Marshy meadow that had been drained for more than 10years experienced an exponential decline in TOC, TN and TP, with decreases of more than 60% for TOC and TN, and 20% for TP. However, after being abandoned for a short time (5years), the TOC, TN and TP concentrations in soil experienced little change because poor water conditions combined with low productivity led to a large loss of soil organic matter. Land use change in the marsh areas has led to a decrease in C/N and C/P ratios of the soil, which are positively related to TOC and TN with different land uses (P<0.05). Marsh reclamation has led to decreasing C/N and C/P ratios in soil and increasing pH values, which are negatively related to TOC, TN and TP (P<0.05). Changes in carbon, nitrogen and phosphorus in soil with different land uses were mainly regulated by water-heat conditions and microbial activity, while the C/N and C/P ratios were mainly regulated by substrate availability. Our results suggest that C/N and C/P ratios and the pH value could be used as indicators to evaluate the quality and nutrient status of wetland soil under different land uses.

Recovery of saturated hydraulic conductivity along a forest successional series from abandoned land to mature, evergreen broad-leaved forest in eastern China

Saturated hydraulic conductivity (Ks) can be used to indicate changes in soil hydrology resulting from vegetation succession. A constant-head permeameter was used to investigate differences in Ks at five soil depths (10, 20, 40, 60, and 80 cm) along a successional sequence of 155 years in evergreen broad-leaved forest at Tiantong National Forest Park, eastern China. The following six forest successional classes were studied: climax evergreen broad-leaved forest (CE), sub-climax evergreen broad-leaved forest (SE), evergreen broad-leaved mixed coniferous forest (MF), coniferous forest (CF), secondary shrub (SS), and abandoned land (AL). Surface Ks (the geometric mean of Ks at 10 and 20 cm soil depths) significantly increased from AL to CE but declined in CF. The surface Ks value under CE was higher than under other successional stages (CE 271 mm h–1, AL 58 mm h–1, SS 124 mm h–1, CF 90 mm h–1, MF 170 mm h–1, SE 231 mm h–1), and was 4.7 times greater than under AL, 2.2 times greater than under SS, and 3.0 times greater than under CF, but showed no significant difference from SE (P &gt; 0.05). Vertical difference of Ks was detected up to a soil depth of 40 cm along forest successional series. Macroporosity was the main determining factor and played an important role in the process of Ks recovery. The likelihood of overland flow generation was inferred by comparing Ks at soil depths of 10, 20, 40, and 60 cm under the various successional stages at prevailing storm intensities. Overland flow was most likely to occur in the early successional stages. This study suggests that Ks could be restored to climax forest levels along forest successional series, but the recovery time could be as long as 95 years.

Carbon mitigation potential of different landuse systems in Northwest Himalayas of India

The alarming increase of CO2 from pre-industrial time has made scientists of every corner to evolve technology to harness this anthropogenic gas and balance the system. A landuse can be a source or sink for carbon depending on the process experienced by the system. The proportion of carbon stored in landuse varies widely depending on their components and climate conditions. More accurate estimates of global or continental CO2 emission from landuse/cover change can only be obtained from extrapolation of reliable local estimates. Northwest Himalayan region has variety of land management practices and landuse systems. In the present research at Department of Silviculture and Agroforestry, Dr. Y. S. Parmar University of Horticulture and Forestry, India, all possible land use systems of Northwestern Himalayas (India) viz. Agri-silvi-horticulture (ASH), Agri-horti-silviculture (AHS), Agri-silviculture (AS), Agri-horticulture (AH), Silvi-pasture (SP), Pure agriculture (PA), Pure grassland (PG) and Abandoned land (AL) / undisturbed lands were taken to assess the relative carbon mitigation (RCM) potential by calculating carbon mitigation in plant biomass as well as in soil component of the system. The carbon inventory in plants were estimated by calculating the above and below ground biomass using non-destructive method for different plant parts while in the soil the carbon expressed as mega grams per hectare (Mg/ha) for soil depths (0-20 cm and 0-40 cm) was computed by multiplying the soil organic carbon (g kg-1) with bulk density (g cm-3) and depth (cm). The results showed that all land use systems had higher relative carbon mitigation potential than agriculture system. For the soil layer 0-20 cm, the relative carbon mitigation potential ranged from 1.33-2.32 (taking value for agriculture LU system as 1). The lowest value was obtained for AH whereas, the maximum for abandoned land. Further, the study shows that the relative carbon mitigation potential of AL was obtained 2.32 times higher than agriculture followed by SP, ASH, AS, PG=AHS and AH. Considering the RCM values for cumulative soil layer 0-40 cm over 0-20 cm only, different land use systems showed slightly higher carbon mitigation potential values except PG. The different land use systems in terms of RCM potential were ranked as: AL &gt; SP &gt; ASH &gt; AS &gt; AH &gt; AHS &gt; PG and ranging from 1.16-2.40.

Land Use Influences Carbon Fluxes in Northern Kazakhstan

A mobile, closed-chamber system (CC) was used to measure carbon and water fluxes on four land-use types common in the Kazakh steppe ecoregion. Land uses represented crop (wheat or barley, WB), abandoned land (AL), crested wheatgrass (CW), and virgin land (VL). Measurements were conducted during the growing season of 2002 in northern Kazakhstan at three locations (blocks) 15–20 km apart. The CC allowed the measurement of the carbon flux components of net ecosystem exchange (NEE), ecosystem respiration (RE) and soil respiration (RS), together with evapotranspiration (ET). Nonlinear regression analyse sw ere used to model gross primary production (GPP) and ET as a function of photosynthetically active radiation (Q); RE and RS were modeled based on air (Tair) and soil (Ts) temperature, respectively. GPP, RE, RS, and ET were estimated for the entire year with the use of continuous 20-min means of Q, Tair, and Ts. Annual NEE indicated that AL gained 536 g CO2 ? m 22 , WB lost 2 191 g CO2 ? m 22 , CW was near equilibrium (2 14 g CO2 ? m 22 ), and VL exhibited considerable carbon accumulation (153 g CO2 ? m 22 ). The lower GPP values of the land-use types dominated by native species (CW and VL) compared to WB and AL were compensated by positive NEE values that were maintained during a longer growing season. As expected, VL and CW allocated a larger proportion of their carbon assimilates belowground. Non–growing-season RE accounted for about 19% of annual RE in all land-use types. The results of this landscape-level study suggest that carbon lost by cultivation of VLs is partially being restored when fields are left uncultivated, and that VLs are net sinks of carbon. Estimations of carbon balances have important management implications, such as estimation of ecosystem productivity and carbon credit certification. Resumen

Effect of land use on soil nutrients in the loess hilly area of the Loess Plateau, China

AbstractUnderstanding the effects of land use change on soil properties is important for soil quality improvement and sustainable land use. In this study, six land use types including wasteland (WLD), cropland (CLD), abandoned land (ABD), artificial grassland (AGD), shrubland (SLD) and woodland (WOD) were selected to analyse the effects of land use types on soil nutrient in the Anjiapo catchment in the western part of the Loess Plateau in China. Significant differences were found in soil organic matter (SOM), total nitrogen (TN) and nitrate nitrogen (NON) (P &lt; 0.01) between the six land use types. Our study also showed that land use types have different effects on soil nutrient storage, and vegetation restoration may improve soil nutrients and soil quality. While crop plantation can significantly decrease soil fertility, the trend can be reversed by cropland abandonment and afforestation. It is recommended that more C input, alternative cultivation practices, vegetation restoration and education and techniques training of local farmers could be used to improve soil conditions and to advance the sustainable land use and local development in the loess hilly area in the Loess Plateau of China. Copyright © 2005 John Wiley &amp; Sons, Ltd.