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The soil NO3− concentration and N2O emissions plays a crucial role in mitigating greenhouse gas emissions and minimizing greenhouse soil degradation concurrently. However, it is essential to understand the extent to which management practices and environmental factors influence the reduction in NO3− concentration and N2O emissions in greenhouse soils. Here, we conducted a meta-analysis, compiling a database of NO3− concentration and N2O emissions in response to either nitrogen or irrigation management in greenhouse vegetable-based systems in China. In summary, controlling the amount of total nitrogen application and irrigation water within specific ranges can effectively reduce both the greenhouse NO3− concentration and N2O emissions. Compared to chemical nitrogen management, the application of slow-release fertilizer could concurrently reduce the soil NO3− concentration and N2O emissions by 0.20 and 0.36 times, respectively. Positive relationships were observed between soil NO3− concentration and N2O emissions under conditions of higher soil organic carbon (OC), total nitrogen (TN), alkali-hydrolyzed nitrogen (AN), and pH, as well as a lower soil temperature (ST) and bulk weight (BW). Under conditions with a higher OC and pH, an appropriate nitrogen application rate is more effective in reducing N2O emissions. While increasing irrigation can reduce soil NO3− concentrations, it also raises the risk of significant NO3− leaching. Overall, nitrogen and irrigation management should be tailored to local soil physicochemical properties to concurrently regulate soil NO3− concentrations and N2O emissions in greenhouse environments. [ABSTRACT FROM AUTHOR]

Microbial communities and their associated enzyme activities affect quantity and quality of phosphorus (P) in soils. Land use change is likely to alter microbial community structure and feedback on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to land use and shifts in the amount and quality of soil phosphorus (P). We investigated effects of the conversion of rainforests into rubber agroforests (AF), young rubber (YR), and mature rubber (MR) plantations on soil P fractions (i.e., labile P, moderately labile P, occluded P, Ca P, and residual P) in Hainan Island, Southern China. Microbial community composition and microbial enzyme were assayed to assess microbial community response to forest conversion. In addition, we also identified soil P fractions that were closely related to soil microbial and chemical properties in these forests. Conversion of forest to pure rubber plantations and agroforestry system caused a negative response in soil microorganisms and activity. The bacteria phospholipid fatty acid (PLFAs) levels in young rubber, mature rubber and rubber agroforests decreased after forest conversion, while the fungal PLFAs levels did not change. Arbuscular mycorrhizal fungi (AMF) (16:1w5c) had the highest value of 0.246 μmol (g OC) − 1 in natural forest, followed by rubber agroforests, mature rubber and young rubber. Level of soil acid phosphatase activity declined soon (5 years) after forest conversion compared to natural forest, but it improved in mature rubber and agroforestry system. Labile P, moderately labile P, occluded P and residual P were highest in young rubber stands, while moderately labile, occluded and residual P were lowest in rubber agroforestry system. Soil P fractions such as labile P, moderately labile P, and Ca P were the most important contributors to the variation in soil microbial community composition. We also found that soil P factions differ significantly among the four transformation systems. Soil labile P faction and its potential sources (moderately labile P, occluded P, and residual P) were positively correlated with NO 3 − , but negatively correlated with AMF, suggesting that these properties play key roles in P transformation. Our study indicated that land use had an impact on microbial community composition and functions, which consequently influenced soil phosphorus availability and cycling. [ABSTRACT FROM AUTHOR]

This study was conducted to determine whether plants in the presence or absence of competition differ in their responses to warming, and whether density modifies the effect of warming. Picea purourea seedlings were grown under ambient and warming (ambient +2.2 °C) conditions in climate control chambers with two different planting densities. After 4 years, seedlings were harvested and measured for height, stem diameter, leaf area, structural biomass, carbon, nitrogen, chlorophyll and carbohydrate levels of needles, branches, stem and roots. At low density, warming increased height, stem diameter, total leaf area biomass production and carbohydrate concentration per seedling, while it decreased C/N ratio for all plant parts, but did not affect chlorophyll content. By contrast, at high density, although warming increased biomass and total leaf area, it did not affect plant height and stem diameter. At the same time, it had different effects on chlorophyll content, C/N ratio and carbohydrate levels among plant parts. On the other hand, high density limited plant growth and altered resource allocation pattern. Our study demonstrates that planting densities decreased the temperature-induced growth enhancement of P. purpurea seedlings and the effects of warming on resource allocation not only showed density-dependence, but also vary with tissue age classes and root diameter; the responses of plants to elevated temperature, acquired from plants growing as individuals, may not be applicable to plants grown under intraspecific competition as typically found in the field. [ABSTRACT FROM AUTHOR]

The conversion of rainforests to plantations leads to about 50% loss in the organic carbon (C) content of the soil and strongly influences nitrogen (N) cycling, potentially increasing greenhouse gas emissions. However, the effect of land-use change in forests on the microbial communities responsible for C and N cycling processes remains poorly understood. This study quantified C and N fractions of soil organic matter in a tropical forest, rubber agroforestry system, 5- and 15-year-old rubber plantations. The community structure and abundance of fungi and bacteria were studied using high-throughput sequencing and q-PCR. Forest conversion substantially altered community structure and abundance of microbial communities. Rainforest conversion to plantation enhanced bacterial diversity and reduced the soil C mineralization rate. In addition, land-use change also enhanced the soil N mineralization rate in 5-year-old rubber plantation and agroforestry system. A structural equation modelling suggested that soil microbial communities played more dominant roles in driving the shift in C and N cycles caused by land-use change than soil C and N pools. These mechanistic insights into the differential control of soil fungal and bacterial communities on C and N mineralization has implications for managing land-use changes in tropical forest ecosystems. • Rainforest conversion into rubber-based plantations decreased soil C and N pools. • Bacterial abundance was reduced but oligotrophic bacteria are less affected by land-use change. • Land-use change increased relative abundance of fungi. • Shifts in the soil bacterial and fungal communities explained ecosystem functions. [ABSTRACT FROM AUTHOR]

Studies on the transformation of P fractions under different land uses and management practices remain scarce, especially in tropical regions. Hence, we investigated the P fraction, microbial communities and soil chemical properties after the conversion of a longan orchard (LO) into an organic tea plantation (OTP) and a conventional tea plantation (CTP) in Hainan, China. At 0–10 cm and 10–20 cm soil depths, the conversion of the LO into the OTP increased the contents of labile P (Resin-P, NaHCO 3 -P i and NaHCO 3 -P o), moderately labile P (NaOH-P i and NaOH-P o) and occluded P (Sonicate-P i and Sonicate-P o) but decreased the contents of Ca-P (HCl-P i) and residual P (stable P), whereas converting the LO into the CTP increased the Ca-P and residual P but decreased the labile P, moderately labile P and occluded P. In addition, at the 0–10 cm soil depth, the bacteria, fungi, actinomycetes, arbuscular mycorrhizal fungal (AMF) and total phospholipid fatty acid (PLFA) biomass were decreased in the CTP, but only the total PLFA was increased in the OTP. However, at the 10–20 cm soil depth, the total PLFA, fungi, and AMF were increased in the OTP, whereas all the PLFA biomarkers remained unchanged in the CTP compared to those in the LO. Furthermore, the labile P, moderately labile P, occluded P and Ca-P in the 0–10 cm layer were related to the soil chemical properties and microbially related groups such as the TK, NO 3 −, NH 4 +, acid phosphatase activity (APA), fungi, AMF and bacteria. However, at the 10–20 cm soil depth, these fractions were only associated with soil chemical properties such as the TK, NO 3 −, NH 4 + and APA. Our results revealed that the land use altered the soil P fractions as well as the microbial biomass and activity related to soil P cycling, and organic management practices enhanced the soil P availability more than conventional management practices. Unlabelled Image • Conversion of longan to tea plantation led to a decline in soil fertility. • Organic management increased soil labile P contents while conventional management increased soil stable P contents. • The biomass of almost all PLFAs were higher in organic tea plantation than conventional tea plantation. • Phosphorus fractions were related to soil chemical properties and microbial related groups, depending on soil depths. [ABSTRACT FROM AUTHOR]