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Alfalfa (Medicago sativa L.) can fix N naturally within soils, which makes alfalfa cultivation useful for enhancing soil fertility while minimizing environmental impacts from pesticides, fertilizers, and soil pollution. To assess the influence of alfalfa cropping on degraded black soil, we determined the nutrient stoichiometry of the soil and soil microbial biomass under four corn cultivation systems at the Harbin Corn Demonstration Base (Heilongjiang, China), which is located in Wujia (126°23′ E, 45°31′ N), Shuangcheng district, Harbin, Heilongjiang Province. The cultivation systems included continuous corn cultivation for more than 30 years (CK), 2 years of alfalfa–corn rotation (AC), three years of alfalfa cropping (TA), and four years of alfalfa cropping (FA). Overall, AC, TA, and FA treatment increased the soil pH, reduced the soil salinity, and increased the organic matter content of the 0–15 cm soil layer. TA and FA presented soil nutrient levels comparable to those of degraded cornfields that were fertilized annually. The TA and FA treatments increased the soil available N:P, soil N:P, and soil C:P ratios. Moreover, TA significantly increased the soil microbial biomass P (SMBP) in the 0–15 cm (surface) soil layer and reduced the soil microbial biomass C (SMBC):SMBP ratio. AC, TA, and FA increased the storage and mineralization rates of soil N and alleviated the microbial P limitations in degraded black soil farmland. Compared with FA, TA resulted in greater improvements in the quality of degraded black soil farmland. The ability of alfalfa to enhance soil fertility makes an important component of sustainable agricultural practices aimed at rehabilitating degraded soils. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) can fix N naturally within soils, which makes alfalfa cultivation useful for enhancing soil fertility while minimizing environmental impacts from pesticides, fertilizers, and soil pollution. To assess the influence of alfalfa cropping on degraded black soil, we determined the nutrient stoichiometry of the soil and soil microbial biomass under four corn cultivation systems at the Harbin Corn Demonstration Base (Heilongjiang, China), which is located in Wujia (126°23′ E, 45°31′ N), Shuangcheng district, Harbin, Heilongjiang Province. The cultivation systems included continuous corn cultivation for more than 30 years (CK), 2 years of alfalfa–corn rotation (AC), three years of alfalfa cropping (TA), and four years of alfalfa cropping (FA). Overall, AC, TA, and FA treatment increased the soil pH, reduced the soil salinity, and increased the organic matter content of the 0–15 cm soil layer. TA and FA presented soil nutrient levels comparable to those of degraded cornfields that were fertilized annually. The TA and FA treatments increased the soil available N:P, soil N:P, and soil C:P ratios. Moreover, TA significantly increased the soil microbial biomass P (SMBP) in the 0–15 cm (surface) soil layer and reduced the soil microbial biomass C (SMBC):SMBP ratio. AC, TA, and FA increased the storage and mineralization rates of soil N and alleviated the microbial P limitations in degraded black soil farmland. Compared with FA, TA resulted in greater improvements in the quality of degraded black soil farmland. The ability of alfalfa to enhance soil fertility makes an important component of sustainable agricultural practices aimed at rehabilitating degraded soils.

Aims: Recent research has suggested that microbial necromass has a disproportionate influence on soil organic C accumulation. But few field studies have followed the bacterial and fungal necromass changes during plant residue decomposition. How bacterial and fungal necromass drives soil C fractions; what role of soil C fractions play; and the critical factors which influence their formation have remained poorly understood. Methods: In a 512-days culture experiment with a perennial C3 herb (St.B, S. bungeana) we traced the formation of muramic acid (MurA) vs. Glucosamine (GluN), and investigated the relationships between MurA, GluN and soil C fractions. Results: The results showed that the bacteria community dominates the decomposition process due to soil pH (> 7) and microbial metabolic C-, P-limitations. The dynamics of bacterial necromass over the time-course of the experiment changed from fluctuating variations to a significant increase. This means that the bacterial necromass has been in a balance of accumulation and decomposition at early and middle periods. Significant accumulation only occurred in the later stages, which was attributed to the involvement of bacteria in more microbial necromass degradation. In this process, the entombing effect of bacterial necromass was more dramatic than their metabolic consumption. While in the case of microbial metabolism limitation, fungal necromass will lose its physicochemical protection of the mineral particles, and thus be degraded and utilized. The priming effecting caused by the one-time input of plant residues with high C/N ratios and soil mineralization resulted in the absence of SOC accumulation in the short term. Microorganisms regulate the turnover of POC, MAOC and MBC by microbial biomass and necromass. The utilization of soil C fractions is the direct cause of SOC decline, while the turnover of microbial necromass only plays an indirect role. Soil pH and microbial biomass stoichiometry as the critical factors in changes in bacterial and fungal necromass. Lower living microbial biomass production and the dynamics of microbial necromass indicate that microbial necromass is constantly broken down as an available C source. Conclusions: With the synergistic effect of soil C fractions, the production of microbial biomass and the degradation of cellular residues maintain microbial stoichiometric homeostasis. In addition to soil pH, microbial biomass stoichiometry co-determines microbial necromass formation. [ABSTRACT FROM AUTHOR]

The effects of different enclosure years on soil physicochemical properties provide scientific basis for soil fertility evaluation and ecological restoration. However, the details on the effects of long-term fencing measures on soil physicochemical properties in alpine regions are still lacking. The soil physicochemical properties, soil nutrient content, and stoichiometric characteristics of desert grassland were examined in the desert steppe of northern Tibetan Plateau, where grazing exclusion using fences has been implemented. This study included conducting experiments on different soil layers during different duration (10, 11, and 12 years) of grazing exclusion using fences; natural plots with no grazing exclusion were used as a control variable. Results showed that several soil physicochemical indexes, such as soil organic matter, soil water content, soil capillary porosity, soil non-capillary porosity, and soil capillary water capacity, in plots under the fencing measures were higher than those in the natural plots. The soil bulk density of the 12- and 11-year grazing exclusion plots was lower than that of the natural plots. The clay content of the 10- and 12-year grazing exclusion plots was higher than that of the natural plots, and the sand content was lower than that of the natural plots. The soil nutrient content was especially low with less than the average level of soil nutrient content in China. The stoichiometric C/N, C/P, N/P, and C/K ratios were 10.28–16.39, 2.74–16.69, 0.24–1.53, and 0.27–0.82, respectively. This result indicates that the degree of organic carbon mineralization was relatively high, and there existed a certain N limitation in the study area. The implementation of enclosure is conducive to the accumulation of C and N. The results provide support for elucidating the physicochemical characteristics, soil nutrients, and nutrient cycling of desert steppe in the northern Tibetan Plateau and for the study of the allotted time of fencing project in the alpine region.

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Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effects of global warming have warmed the climate of the Qinghai-Tibetan Plateau (QTP) leading to changes in plant growth and soil nutrients in the alpine meadows. However, few studies have addressed the effects of warming on plant allometric growth and soil stoichiometry in these meadows on a long-term scale. Therefore, the effects of soil stoichiometry on plant allometric growth remain unclear under long-term warming in the alpine meadows. This study adopted infrared radiators to conduct an 8-year warming experiment in a permafrost region on the QTP starting in 2010, and surveyed growth indices of the plant community during the growing season. Soil organic carbon (C), total nitrogen (N), and total phosphorus (P) in an alpine meadow were measured. We initially learned that the aboveground part of the alpine meadow vegetation in the warming treatment changed from an isometric to an allometric growth pattern while the allometric growth pattern of the belowground part was further strengthened. Second, the contents of soil C, N, and P decreased at the 0–20 cm depth and increased at the 20–30 cm depth in warming. The ratios of soil C:N, C:P, and N:P showed increasing trends at different soil depths with artificial warming, and their amplitudes increased with soil depths. Warming promoted the migration of soil stoichiometric characteristics of C, N, and P to deep soil. Finally, the correlations of plant growth with soil stoichiometric characteristics were weakened by warming, demonstrating that the downward migration of soil stoichiometric characteristics to deep soil in warming had effects on the growth of vegetation in the alpine meadow. It concludes that the change in soil stoichiometric characteristics with soil depths promotes plant allometric growth in the alpine meadow under climate warming. [ABSTRACT FROM AUTHOR]

The effects of global warming have warmed the climate of the Qinghai-Tibetan Plateau (QTP) leading to changes in plant growth and soil nutrients in the alpine meadows. However, few studies have addressed the effects of warming on plant allometric growth and soil stoichiometry in these meadows on a long-term scale. Therefore, the effects of soil stoichiometry on plant allometric growth remain unclear under long-term warming in the alpine meadows. This study adopted infrared radiators to conduct an 8-year warming experiment in a permafrost region on the QTP starting in 2010, and surveyed growth indices of the plant community during the growing season. Soil organic carbon (C), total nitrogen (N), and total phosphorus (P) in an alpine meadow were measured. We initially learned that the aboveground part of the alpine meadow vegetation in the warming treatment changed from an isometric to an allometric growth pattern while the allometric growth pattern of the belowground part was further strengthened. Second, the contents of soil C, N, and P decreased at the 0–20 cm depth and increased at the 20–30 cm depth in warming. The ratios of soil C:N, C:P, and N:P showed increasing trends at different soil depths with artificial warming, and their amplitudes increased with soil depths. Warming promoted the migration of soil stoichiometric characteristics of C, N, and P to deep soil. Finally, the correlations of plant growth with soil stoichiometric characteristics were weakened by warming, demonstrating that the downward migration of soil stoichiometric characteristics to deep soil in warming had effects on the growth of vegetation in the alpine meadow. It concludes that the change in soil stoichiometric characteristics with soil depths promotes plant allometric growth in the alpine meadow under climate warming.

Copyright of Acta Prataculturae Sinica is the property of Acta Prataculturae Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)