Biology and Fertility of Soils

Chúng tôi đã nghiên cứu hoạt tính phosphatase acid (APA) và mối quan hệ của nó với một số tính chất lý hóa của đất dọc theo gradient rừng mùa nước nổi. Mẫu đất được thu thập trong thời gian không ngập lụt tại ba khu vực chịu ảnh hưởng của các thời gian ngập khác nhau: khu vực ngập 8 tháng mỗi năm (MAX), khu vực ngập 5 tháng mỗi năm (MED) và khu vực ngập 2 tháng mỗi năm (MIN). Tại khu vực MAX, APA có giá trị thấp và có mối tương quan âm với phân đoạn đất mịn. Trong khu vực này, các khoáng chất đất sét có vẻ như giảm hoạt tính enzym. Tại khu vực MIN, phosphatase acid có hoạt tính tương đối cao hơn, có mối tương quan dương với hàm lượng carbon hữu cơ trong đất và với Al liên kết với chất hữu cơ. Giá trị cao nhất của APA được ghi nhận ở khu vực MED, và không tìm thấy mối tương quan nào giữa các yếu tố đất và hoạt tính enzym trong khu vực này. Tuy nhiên, kết quả của chúng tôi chỉ giới hạn ở một mốc thời gian thu thập mẫu đơn lẻ và do đó, không xem xét được sự động học theo mùa của phosphatase acid liên quan đến các yếu tố đất khác theo thời gian.

With P being a non-renewable resource, the use of microbial inoculants and waste products for more efficient and sustainable P use in plant production has been proposed. We investigated the ability of Penicillium bilaii to mobilize P in a low-fertility soil with or without amendment of sewage sludge as additional P source. Maize was grown for 27 days in rhizoboxes enabling studies of root growth in addition to plant and soil parameters. P. bilaii was inoculated either at the seed or the sewage sludge patch. At early growth stages, P. bilaii inoculation of seeds increased maize shoot length. However, at the end of experiment, the effect had ceased. Root growth was increased by seed P. bilaii inoculation alone and in combination with sewage sludge, whereas patch inoculation was less effective. Colonization studies performed at harvest showed that P. bilaii could not be detected in the maize rhizosphere but stayed at the place of inoculation. In sewage sludge patches, the growth of Penicillium strains other than P. bilaii was stimulated; hence, using sewage sludge for combined P resource and carrier of microbial inoculants is discussed. Unexpectedly, the greater root development of seed-inoculated plants did not result in increased plant P uptake and neither did inoculation at the sewage sludge patch. This study raises the question if the soil P status can be too low for a beneficial effect of additional early root growth and thus a beneficial effect of seed inoculation of P. bilaii.

A field experiment was conducted to evaluate the combined or individual effects of biochar and nitrapyrin (a nitrification inhibitor) on N2O and NO emissions from a sandy loam soil cropped to maize. The study included nine treatments: addition of urea alone or combined with nitrapyrin to soils that had been amended with biochar at 0, 3, 6, and 12 t ha−1 in the preceding year, and a control without the addition of N fertilizer. Peaks in N2O and NO flux occurred simultaneously following fertilizer application and intense rainfall events, and the peak of NO flux was much higher than that of N2O following application of basal fertilizer. Mean emission ratios of NO/N2O ranged from 1.11 to 1.72, suggesting that N2O was primarily derived from nitrification. Cumulative N2O and NO emissions were 1.00 kg N2O-N ha−1 and 1.39 kg NO-N ha−1 in the N treatment, respectively, decreasing to 0.81–0.85 kg N2O-N ha−1 and 1.31–1.35 kg NO-N ha−1 in the biochar amended soils, respectively, while there was no significant difference among the treatments. NO emissions were significantly lower in the nitrapyrin treatments than in the N fertilization-alone treatments (P < 0.05), but there was no effect on N2O emissions. Neither biochar nor nitrapyrin amendment affected maize yield or N uptake. Overall, our results showed that biochar amendment in the preceding year had little effect on N2O and NO emissions in the following year, while the nitrapyrin decreased NO, but not N2O emissions, probably due to suppression of denitrification caused by the low soil moisture content.

Degradation of the recalcitrant polyphenolic plant residue lignin is a bottleneck of element turnover in terrestrial ecosystems. Consequently, there is a great interest to understand underlying mechanisms and dynamics, considering the possible ecological roles of soils as sinks or sources of carbon dioxide. The present review provides a critical, holistic view of the ecological importance of the degradation of recalcitrant residues attributed to laccase-producing soil microbes and laccase activity under different environmental conditions. We synthesize and discuss the results of previous classical ecological, enzymatic, and molecular-ecological studies to point out discrepancies between gene detection, enzyme activity, and substrate degradability. We single out major hindrances to current research and outline a progression toward a better understanding of laccase activity by fungi in soil ecosystems.

A short-term in situ 15 N labeling experiment was conducted to investigate whether the N uptake and preference for different forms of available soil N for dominant plant species and soil microorganisms relate to the plant community productivity change at the no degradation stage, early stage of degradation, and late stage of degradation in an alpine meadow on the Qinghai-Tibetan Plateau. At the early stage of degradation in the alpine meadow, aboveground net primary productivity decreased, while belowground net primary productivity increased. As a result, the total net primary productivity was unchanged at the early stage of degradation. Both aboveground and belowground net primary productivity significantly decreased at the late stage of degradation compared with the non-degraded meadows. Plants and microorganisms mainly absorbed inorganic N and preferred NH4+ at the non-degraded meadows where available soil N (the total concentration of exchangeable NH4+, NO3−, and dissolved organic N) was maintained at a high level of 60.9 μg N g−1 dry soil, indicating an N-use chemical niche overlap. Plants and microorganisms showed a niche differentiation at the early stage of degradation where available soil N decreased to a medium level of 44.6 μg N g−1 dry soil; plants preferred NO3−, while microorganisms took up more NH4+. In contrast, microorganisms increased their uptake of organic N, while plants assimilated more inorganic N, indicating that plants and microorganisms showed a niche differentiation where available soil N decreased to a low level of 26.6 μg N g−1 dry soil at the late stage of degradation. The higher N uptake (30% increase of N uptake compared with non-degraded meadows) of dominant plant species and niche differentiation in using available soil N between plants and microorganisms are two mechanisms maintaining the total community net primary productivity, even when available soil N decreased at the early stage of degradation. Plants and microorganisms also showed a niche differentiation when available N declined further at the late stage of degradation. However, the N uptake by dominant plant species greatly declined at the late stage of degradation (76% reduction of N uptake compared with non-degraded meadows), which might explain the community net primary productivity reduction (78% lower compared with non-degraded meadows).

To find wide host range compatible potential inoculant strains with high efficiency in N fixation, we isolated rhizobia from soybean root nodules in Sichuan. Most of the isolated rhizobia were no- or low-effective strains. Eight out of 75 isolates promoted significantly the growth of soybean cultivar Gongxuan No. 1. When tested with three more soybean cultivars, the isolates assigned as Bradyrhizobium japonicum SCAUs36, Bradyrhizobium diazoefficiens SCAUs46, and Ensifer fredii SCAUs65 promoted significantly (P < 0.05) the growth of each cultivar. The nodC and nifH genes of bradyrhizobial SCAUs36 and SCAUd46 and E. fredii SCAUs65 grouped together with those of broad host range strains. In field experiments with two more soybean cultivars, B. diazoefficiens SCAUs46 and E. fredii SCAUs65 performed well both in mild and hot-dry climates, implying that the isolates were potential inoculants to be applied in diverse soil and climate conditions.

Nitrogen fixation in seven groundnut genotypes was measured by 15N-isotope dilution using a non-nodulating cultivar of groundnut as the nonfixing reference plant. Nitrogen fixation varied between 100 kg N ha−1 in genotype J-11 and 153 kg N ha−1 in Robut 33-1. The amount of plant-available soil N was small, so that 86%–92% of plant nitrogen was derived from N2-fixation. Thus differences in N2-fixation between genotypes closely reflected differences in their total N accumulation.

The influence of surface growth of inoculated cyanobacteria (blue-green algae) on subsurface properties of a brown earth, silt loam soil was studied in reconstituted flooded soil columns. One blue-green algae species, Nostoc muscorum, become dominant within the first 7 days of inoculation. In light control columns (not inoculated) a bryophyte, Barbula recurvirostra, was dominant although significant growth of indigenous blue-green algae occurred. The blue-green algae counts were in the range of 1×106 g-1 dry soil in the surface layer (0–0.7 cm) in both columns. Any effect of surface phototrophic growth on soil properties was restricted to the surface layer. In inoculated columns there was a twofold increase in microbial biomass and an eightfold increase in bacterial numbers by week 13. However, bacterial numbers declined so that there was only a 2.8-fold increase by week 21. Dehydrogenase (x2.1), urease (x2.8) and phosphatase (x3.1) activities and polysaccharides (+69%) increased by week 21 as a result of the blue-green algae inoculation along with a significant improvement in soil aggregation. However, similar increases occurred in the light control columns, indicating that given appropriate conditions of light and moisture indigenous species may be ultimately as effective as introduced species in bringing about biochemical and microbiological changes to soil.