Subtropical Region Of China Research Articles

Simulated nitrogen deposition reduces potential nitrous oxide emissions in a natural Castanopsis carlesii forest soil

The reactive nitrogen deposition in subtropical region of China has been increasing annually, which affects biogeochemical processes in forest soils. In this study, three treatments were established, including control (no N addition, CK), low nitrogen deposition (40 kg·hm-2·a-1, LN), and high nitrogen deposition (80 kg·hm-2·a-1, HN) to study the response of denitrifying functional genes and potential N2O emissions to simulated nitrogen deposition in the soils of a natural Castanopsis carlesii forest. Results showed that HN significantly decreased soil potential N2O emission, while 8-year nitrogen deposition did not affect the abundances of nirS, nirK, nosZ Ⅰ and nosZ Ⅱ. However, the abundance of nosZ Ⅰwas significantly higher than nosZ Ⅱ in all the treatments, indicating that nosZ Ⅰ dominated over nosZ Ⅱ in the acidic soils. HN significantly decreased the ratio of (nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ), which was positively correlated with soil pH. The results suggested that long-term high nitrogen deposition reduced soil pH and the abundance ratio of (nirK+nirS)/(nosZ Ⅰ+nosZ Ⅱ), which subsequently reduced the potential N2O emission.

Temporal Changes in Growth–Climate Relationship of Pinus taiwanensis Hayata in Subtropical China

Whether the tree growth–climate relationship is consistent in subtropical China has not yet been reported. To fill this gap, we chose Pinus taiwanensis which grow on Lushan Mountain in a subtropical region of China as the target tree species, established a standard tree-ring width chronology, and conducted a moving correlation analysis with climatic factors. The results showed that the relationship between radial growth of P. taiwanensis and climate changed significantly during 1980–1990. From 1955 to 1985, tree rings were negatively affected mainly by precipitation in September of the current growing season. From 1990 to 2014, however, a significant negative correlation appeared between tree rings and sunshine duration from March to April in the growing season. Our results suggest the need to pay attention to this growth–climate inconsistency when conducting dendroclimatology studies in subtropical China. However, the causes of the inconsistency still require further confirmation.

Contrasting water-use patterns of Chinese fir among different plantation types in a subtropical region of China.

Plantation cultivation plays an important role in improving terrestrial ecosystem functions and services. Understanding the water-use patterns of major afforestation species is vital for formulating ecological restoration strategies and predicting the response of plantation to climate change. However, the impacts and drivers of forest types on water-use patterns of key tree species are poorly understood. Here, the combined methods of dual stable isotope of δD and δ18O and Bayesian mixed framework (MixSIAR) were employed to investigate the water-use patterns of Cunninghamia lanceolata (Chinese fir) in a monoculture, mixed forest with Cinnamomum camphora, and mixed forest with Alnus cremastogyne under different rainfall events in subtropical China. Furthermore, the relative contribution of different soil and plant factors to the water-use patterns of Chinese fir was quantified using a random forest model. Our results showed that Chinese fir in the mixed forests (with C. camphora or with A. cremastogyne) utilized less water from shallow soil compared to that in a monoculture but significantly improved the proportion of water absorbed from deep soil with the increase of 55.57%–64.90% and 68.99%–108.83% following moderate and heavy rainfall events, respectively. The most important factors contributing to the differences in water-use patterns of Chinese fir among monoculture and mixed forests were tree attributes (i.e., leaf biomass, eco-physiological regulation, and fine root biomass). These findings reveal that Chinese fir in mixed forests could optimize water-use patterns by adjusting plant properties for interspecific niche complementarity, improving the utilization of deep soil water. Overall, this study suggests that mixed-species plantations could improve water-use efficiency and reduce the sensitivity of tree species to precipitation change, indicating they are better able to cope with expected climate variability.

Responses of soil microbial biomass and carbon source utilization to simulated nitrogen deposition and drought in a Cunninghamia lanceolata plantation

Chinese fir (Cunninghamia lanceolata) plantation is a dominant forest type and carbon sink in the subtropical region in China. An experiment with simulated nitrogen deposition (addition of 40 kg N·hm-2·a-1) and drought (50% of precipitation exclusion, PE) was established in Chinese fir plantation in 2018. Soil samples (0-15 cm) were collected in summer (July 2020) and winter (January 2021). Soil microbial biomass, colony forming units (CFUs) and carbon source utilization were determined through phospholipid fatty acids (PLFAs), plate count, and Biolog methods, respectively. The results showed significant seasonal variations of PLFAs-related microbial biomass and composition. Soil bacterial and fungal CFUs tended to be decreased by nitrogen addition or precipitation exclusion treatment, and bacterial CFUs were more sensitive to the two treatments than fungal CFUs. Soil microbial function (i.e. carbon source utilization) was not affected by nitrogen addition, but significantly decreased by precipitation exclusion. There was a significant positive correlation between bacterial CFUs and microbial function, indicating the crucial roles of culturable bacteria in microbial carbon transformation. Our results highlight the critical effects of nitrogen deposition and 50% reduced precipitation on microbes in topsoil of fir plantation, with implications for unraveling soil microbial ecological function of subtropical forest ecosystem under global changes in future.

Contributions of Climate Change, Vegetation Growth, and Elevated Atmospheric CO2 Concentration to Variation in Water Use Efficiency in Subtropical China

Ecosystem water use efficiency (WUE) plays an important role in maintaining the carbon assimilation–water transpiration balance in ecosystems. However, spatiotemporal changes in WUE in the subtropical region of China (STC) and the impact of driving forces remain unclear. In this study, we analyzed the spatiotemporal variation in WUE in the STC and used ridge regression combined with path analysis to identify direct and indirect effects of climate change, vegetation growth, and elevated atmospheric CO2 concentration (Ca) on the interannual trend in WUE. We then quantified the actual and relative contributions of these drivers to WUE change based on the sensitivity of these variables on WUE and the trends of the variables themselves. Results reveal a mean WUE of 1.57 g C/m2/mm in the STC. The annual WUE series showed a descending trend with a decline rate of 0.0006 g C/m2/mm/year. The annual average temperature (MAT) and leaf area index (LAI) had strong positive direct effects on the WUE, while the vapor pressure deficit (VPD) had a strong negative direct effect. Opposite direct and indirect effects offset each other, but overall there was a total positive effect of Ca and VPD on WUE. In terms of actual contribution, LAI, Ca, and VPD were the main driving factors; LAI caused WUE to increase by 0.0026 g C/m2/mm/year, while Ca and VPD caused WUE to decrease by 0.0021 and 0.0012 g C/m2/mm/year, respectively. In terms of relative contribution, LAI dominated the WUE trend, although Ca and VPD were also important factors. Other drivers contributed less to the WUE trend. The results of this study have implications for ecological management and restoration under environmental climate change conditions in subtropical regions worldwide.

Soil quality and r – K fungal communities in plantations after conversion from subtropical forest

Intensive clear-cutting of natural forests and conversion to monoculture plantations are ongoing worldwide, leading to the degradation of soil quality and microbial functions. Here, we compared soil quality index (SQI) and fungal communities in a natural forest (Forest) and four 5-year-old monoculture plantations, including Camellia oleifera (Oil), Amygdalus persica (Peach), Myrica rubra (Berry) and Cunninghamia lanceolate (Fir) in a subtropical region of China. After conversion, soil pH in the plantations rose up to 0.31, but organic carbon and total nitrogen contents, sucrase, acid protease, glutaminase, acid and alkaline phosphatase activities decreased by 83%, 59%, 40%, 64%, 66%, 94% and 59%, respectively. Correspondingly, the SQI dropped by 65%. High-throughput sequencing of the ITS1 region demonstrated an increase in α-diversity and a striking difference in β-diversity of fungi following conversion. Changes in the dominant fungal taxa following forest conversion to plantations were interpreted by r- and K-selection of life strategies. Conversion increased the fungal groups with r-strategies, such as Ascomycota and Zygomycota, but decreased the fungal groups with K-strategies, such as Basidiomycota. Genera affiliated to those phyla including Pseudophialophora, Rhytisma increased, but Russula decreased. Redundancy analysis and structural equation modeling indicated that the diversity and composition of fungal communities changed with soil degradation, which was mainly driven by increased pH and total phosphorus content, but decreased C/N ratio and C and N related enzymes activities. Overall, the conversion of forest to monoculture plantations decreased soil quality and the abundance of K-strategists, retarded the decomposition of persistent organic matter, but boosted the prevalence of r-strategists in a more diverse fungal community.

Land-use-driven change in soil labile carbon affects microbial community composition and function

The conversion of natural forests to plantations can lead to a substantial loss of soil organic carbon (SOC) and threaten the function of soil microbial communities. However, the effect of forest conversion on the relationship between SOC dynamics and shifts in the composition and function of the microbial community remain poorly understood, although such information is critical for predicting the long-term effect of land-use change on global SOC dynamics and storage. To fill this knowledge gap, our study investigated the influence of two decades of converting natural forest to a tea plantation on SOC storage, microbial community composition, C-degrading enzyme activity and the abundance of C-degrading microbial functional genes in a subtropical region in China. Two decades after converting natural forest to tea plantation, SOC storage decreased by 30%, and labile SOC [including easily mineralized C (Cmin), readily oxidizable C (ROC), dissolved organic C (DOC), and microbial biomass C (MBC)] decreased by 21–71%. Land-use change decreased the relative abundance of copiotrophic bacteria but increased the relative abundance of oligotrophic bacteria and lignin-degrading fungi. This resulted in a decrease in cellulase activity and cbhI gene abundance involved in cellulose degradation and conversely an increase in ligninase activity involved in lignin degradation after the conversion. Such shifts in microbial community composition and function associated with land-use change were mediated by the decrease in the labile C pool rather than the total SOC. Our study provided new insights into not only shifts in microbial communities but also specific C functional genes and related enzymes after forest conversion. These findings highlight that labile SOC, as an important functional soil component for microbial communities, significantly affects SOC dynamics and storage.

First Report of Tobacco Mosaic Virus Infecting Papaya in China.

Papaya (Carica papaya. L) is widely cultivated in tropical and subtropical regions of China and has high nutritional and medicinal values. More than 11 species of papaya viruses have been recorded in the world, but the most destructive one for papaya production in China is papaya ringspot virus (PRSV) (Li, 2019). In order to control PRSV, a transgenic papaya cultivar, designated as 'Huanong No.1', carrying the nuclear inclusion b (Nib) cistron of PRSV Ys isolate, was successfully commercialized in 2006, and has shown a wide range of resistance to PRSV in China (Li et al. 2007). However, more than 10% of 'Huanong No.1' plants developed different virus-like symptoms on leaves, including mosaic, yellow mottle, and deformation in some plantations of Guangdong Province, China in 2020 (Suppl Figure 1a, b, and c). Based on observation of the symptomatic phenotypes, the field surveys indicated that the disease incidence ranged from 10% to 40%, resulting in significant loss of papaya fruit. The virus particles were purified from symptomatic papaya plants following Gooding and Hebert (1967) and rigid filamentous particles resembling tobacco mosaic virus (TMV) were observed by transmission electron microscopy. Purified virus samples were further utilized to mechanically inoculate healthy seedlings of papaya, Nicotiana glutinosa and N. tabacum K326. At 15 days after inoculation, the obvious symptoms of virus infection on different plants were observed. The diseased plants showed systemic mottling and mosaic in the papaya leaves (Suppl Figure 1d), necrotic spots on the leaves of N. glutinosa (Suppl Figure 1e), mosaic and mottling spots on leaves of N. tabacum K326 (Suppl Figure 1f). These symptoms produced on the hosts were exactly the same caused by TMV. In order to reconfirm the species of the infected virus, the total RNA was extracted from the single leaf of 30 diseased papaya plants using RNAiso Plus kit (Takara, Japan) and reverse transcription--polymerase chain reaction was performed using TMV coat protein cistron specific primers (TMV-CP-R: 5'-TCAAGTTGCAGGACCAGA-3' and TMV-CP-F 5'- ATGTCTTACAGTATCACTAC-3') as described previously (Srivastava et al. 2015). An expected 480-bp fragment was amplified from all of the samples. Sequence analysis revealed that the diseased papaya was infected with TMV, designated as Cpa-TMV. In order to understand the difference among TMV isolates on papaya and other host plants, the whole genomic sequence of TMV from papaya was obtained and analyzed. The total length of the genome of Cpa-TMV was 6395 bp, and the sequence was submitted to the NCBI database (GenBank no. OK149218). A neighbor-joining phylogenetic tree of 19 TMV isolates was constructed using MEGA X software. Phylogenetic analysis indicated that the 19 TMV isolates were divided into Clade I, II and III (Suppl Figure 2). Interestingly, Clade I was composed of 12 Chinese mainland isolates, which further was grouped into IA (Northern China) and IB (Southern China), while 6 isolates from other countries and 1 isolate (pet-TMV) from China Taiwan belong to Clade II and III. It is inferred that the TMV isolates from Chinese mainland are quite different from other countries and China Taiwan. This suggests that geographical differences between Northern and Southern China may lead to the gradual differentiation of TMV isolates and eventually induce those isolates to evolve into two subclades. To our knowledge, this is the first report of TMV infection on papaya under natural conditions. It is necessary to find effective methods to control TMV in transgenic papaya.

Predicting suitable habitats of Melia azedarach L. in China using data mining

Melia azedarach L. is an important economic tree widely distributed in tropical and subtropical regions of China and some other countries. However, it is unclear how the species’ suitable habitat will respond to future climate changes. We aimed to select the most accurate one among seven data mining models to predict the current and future suitable habitats for M. azedarach in China. These models include: maximum entropy (MaxEnt), support vector machine (SVM), generalized linear model (GLM), random forest (RF), naive bayesian model (NBM), extreme gradient boosting (XGBoost), and gradient boosting machine (GBM). A total of 906 M. azedarach locations were identified, and sixteen climate predictors were used for model building. The models’ validity was assessed using three measures (Area Under the Curves (AUC), kappa, and overall accuracy (OA)). We found that the RF provided the most outstanding performance in prediction power and generalization capacity. The top climate factors affecting the species’ suitable habitats were mean coldest month temperature (MCMT), followed by the number of frost-free days (NFFD), degree-days above 18 °C (DD > 18), temperature difference between MWMT and MCMT, or continentality (TD), mean annual precipitation (MAP), and degree-days below 18 °C (DD < 18). We projected that future suitable habitat of this species would increase under both the RCP4.5 and RCP8.5 scenarios for the 2011–2040 (2020s), 2041–2070 (2050s), and 2071–2100 (2080s). Our findings are expected to assist in better understanding the impact of climate change on the species and provide scientific basis for its planting and conservation.

Plants, soil properties and microbes directly and positively drive ecosystem multifunctionality in a plantation chronosequence

AbstractChinese fir (Cunninghamia lanceolata) is the main plantation species in the subtropical region of China. However, the shift in ecosystem multifunctionality with stand development remains largely unexplored for these plantations. This study used a chronosequence to investigate the variations of ecosystem multifunctionality by employing individual functions and identified its driving factors in Chinese fir plantations. The findings provide strong evidence that the individual functions of carbon stocks, water regulation and wood production increased with stand ages, but the tradeoff of individual functions did not significantly increase ecosystem multifunctionality. Soil microbial parameters (the abundances of bacteria, fungi and actinomycete), soil properties (soil moisture, total carbon and total nitrogen), and plant parameters (the shrub layer cover and total understory cover) exhibited positive correlations with ecosystem multifunctionality. The structural equation model revealed that plants, soil properties and microbes pathways explained 83% of the total variance in ecosystem multifunctionality. Results showed that plants, soil microbes and properties directly and significantly affected ecosystem multifunctionality with path coefficients of 0.404, 0.487 and 0.334, respectively. Soil microbes were identified as the top direct predictor for ecosystem multifunctionality, while plant and soil properties had strong direct and positive effects on ecosystem multifunctionality. These results verified that soil microbes, plants and soil properties directly and positively regulated ecosystem multifunctionality. Our findings demonstrate that ecosystem multifunctionality should be considered as a comprehensive ecological indicator for ecosystem services and functions, and sustainable plantation management. This study highlights the importance of conserving soil microbes for maintaining multifunctionality in Chinese fir plantations.

Identification and Characterization of Calonectria Species Associated with Plant Diseases in Southern China.

Calonectria species are important plant pathogens on a wide range of hosts, causing significant losses to plant production worldwide. During our survey on phytopathogenic fungi from 2019 to 2021, diseased samples were collected from various hosts in Guangdong Province, China. In total, 16 Calonectria isolates were obtained from leaf spots, stem blights and root rots of species of Arachis, Cassia, Callistemon, Eucalyptus, Heliconia, Melaleuca and Strelitzia plants. Isolates were identified morphologically, and a multigene phylogenetic analysis of combined partial sequences of calmodulin (cmdA), translation elongation factor 1-alpha (tef1-α) and beta-tubulin (β-tubulin) was performed. These sixteen isolates were further identified as nine Calonectria species, with five new species: Ca. cassiae, Ca. guangdongensis, Ca. melaleucae, Ca. shaoguanensis and Ca. strelitziae, as well as four new records: Ca. aconidialis from Arachis hypogaea, Ca. auriculiformis from Eucalyptus sp., Ca. eucalypti from Callistemon rigidus, and Ca. hongkongensis from Eucalyptus gunnii. Moreover, we provide updated phylogenetic trees for four Calonectria species complexes viz. Ca. colhounii, Ca. cylindrospora, Ca. kyotensis and Ca. reteaudii. Our study is the first comprehensive study on Calonectria species associated with various hosts from subtropical regions in China. Results from the present study will be an addition to the biodiversity of microfungi in South China.

Responses of soil ammonia-oxidizing microorganisms to simulated nitrogen deposition in a natural Castanopsis carlesii forest

Subtropical region of China is one of the global hotspots receiving nitrogen deposition. Nitrogen deposition could affect the abundance and community structure of ammonia oxidizers including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and complete ammonia oxidizer (comammox Nitrospira), with consequences on soil nutrient cycling that are driven by microorganisms. There is limited understanding for the newly discovered comammox Nitrospira in the subtropical forest soils. Here, we investigated the effect of simulated N deposition on abundances of soil ammonia oxidizers in the Castanopsis fargesii Nature Reserve in Xinkou Town, Sanming City, Fujian Province, China. Soil samples were collected from the field plots which received long-term nitrogen deposition with different dosages, including: CK, no additional treatment; LN, low nitrogen deposition treatment, dosage of 40 kg N·hm-2·a-1; and HN, high nitrogen deposition treatment, dosage of 80 kg N·hm-2·a-1. After 8-year treatment, simulated N deposition decreased soil pH and organic matter content, and increased nitrate content. We failed to amplify the amoA gene of AOB in the tested soils. High nitrogen deposition increased the abundance of AOA, but did not affect the abundance of comammox Nitrospira clade A and clade B. The ratio of comammox Nitrospira to AOA decreased with N addition, indicating that N addition weakened the role of comammox Nitrospira in nitrification in the subtropical forest soils. However, there were strong non-specific amplifications for both comammox Nitrospira clades A and B, highlighting the demand for the development of high coverage and specificity primers for comammox Nitrospira investigations in the future. The abundance of comammox Nitrospira clade A was positively correlated with total nitrogen (TN) and NH4+ concentration, while that of clade B was positively associated with soil organic carbon (SOC), TN and NH4+ Concentration. Overall, our findings demonstrated that simulated N deposition increased the relative importance of AOA in nitrification in the natural Castanopsis carlesii forest soil. These findings could provide theoretical support in coping with global change and N deposition in these regions.

Changes in Carbon Storage of Masson Pine Forests along a Latitudinal Gradient with Different Stand Structures in Southern China

The spatial patterns of carbon pool in landscape vary greatly with variation of forest structures and climate conditions. In this field study, the carbon storage in overstory, understory, litter layer of plants and soil carbon in forests was investigated in 26-28 year-old Masson pine (Pinus massoniana) pure and mixed forests along a latitudinal gradient (20–30 °N) crossing Hunan and Guangxi provinces of China, during the period of May 2015–August 2017. We found that the total carbon storage in Masson pine forests ranged 88.92–149.41 Mg/ha, of which 54.03% occurred in aboveground compound and 45.97% occurred belowground. The overall total carbon storage distribution was 34.62–68.72 Mg/ha, 3.82–10.19 Mg/ha, 2.37–3.96 Mg/ha, and 6.06–12.08 Mg/ha in stems, branches, leaves, and roots, respectively. The carbon storage in the overstory of forest stands and forest soils significantly decreased with increasing latitude, while the carbon storage in the understory and litter of the forest stands significantly increased as the latitude increased. The overall carbon storage significantly decreases by 8.26 Mg/ha in Masson pine forests as the latitude increased by one degree. The carbon storage increased by 8.43% in Masson pine mixed forests compared to the pure forest stands after the transformation from the pure forest stands into the mixed forest stands ∼ 15 years later. The results of changes in carbon storage in the studied forests with the latitudinal gradient could be attributed to variations in hydrothermal conditions with changing latitudes. The forest structure with different tree species composition was another important factor regulating carbon storage in forest ecosystems at the same latitude. The results provided a scientific basis for better understanding of latitudinal variation and spatial distribution of carbon storage in Masson pine forest stands with optimal forest stand structures in subtropical region of China.

Initial ecological restoration assessment of an urban river in the subtropical region in China

Rivers in urbanised cities are often polluted, black, and odorous, with poor water quality and deteriorated ecology. Despite many river restoration studies, assessments of ecological responses to river restoration practices remain scant. Benthic animals are useful biological indicators showing the change and succession of river ecosystems; however, previous studies have mainly focussed on a few target species without considering overall ecosystem integrity. Here, we used a multi-index biological assessment method, benthic index of biological integrity (B-IBI) to assess ecological responses to river restoration of the Shahe River in subtropical region of China. Spatiotemporal changes in the macrobenthos community structure after restoration were monitored to explore species succession. We found that the number of macrobenthos species increased from 16 to 42, with the emergence of some pollution-sensitive species during the restoration period. Molluscs showed widespread recovery, and their relative proportions almost doubled from 12.5% to 24.4%. Oligochaetes and chironomids were the pioneer species in the recovering communities, while gastropod molluscs and pollution-sensitive aquatic insects were transitional species that first settled during the initial recovery period. Based on our survey data, 25 candidate metrics were selected, and five core metrics (total taxa, Simpson diversity index, percentage of crustaceans and molluscs, percentage of predators, and percentage of collector-gatherers) were identified after screening to establish the B-IBI. Our analysis revealed a distinct improvement in the overall health of the river, with the proportions of “excellent” and “good” sites increasing from zero to 28.6% and from 14.3% to 42.9%, respectively. A correlation analysis indicated that water flow, molluscs, and total phosphorus content were the three drivers of ecological recovery in the Shahe River. Overall, our study demonstrates the importance of governance and restoration of rivers in tropical and subtropical cities, and provides valuable evidence that can guide the design and evaluation of river restoration works.

First report of Nigrospora lacticolonia causing leaf spot of Bougainvillea spectabilis in China

Bougainvillea spectabilis is an ornamental shrubby vine widely distributed in tropical and subtropical regions of China. In September 2020, a leaf spot of B. spectabilis was observed on Yongxing Island of Sansha City, Hainan Province. At a disease incidence of >30%, this leaf spot seriously reduced the ornamental value of affected plants. The typical symptoms included lesions consisting of circular or subcircular, gray pale centers with dark brown borders surrounded by diffused yellow margins. Fungal cultures isolated from colonies growing from surface-sterilized leaf tissues on potato dextrose agar exhibited similar morphological characteristics. The fungus was identified as Nigrospora lacticolonia based on its morphological characteristics and phylogenetic analysis using the internal transcribed spacer (ITS) region of rDNA, β-tubulin (TUB2) and translation elongation factor 1-alpha (TEF1-α) gene sequences. Pathogenicity tests showed that the fungus could infect B. spectabilis, and it was successfully re-isolated from inoculated leaf tissues, fulfilling Koch’s postulates. This is the first report of N. lacticolonia causing leaf spot on B. spectabilis.

Evaluation of pedotransfer functions for predicting particle density of soils with low organic matter contents

Soil particle density (ρs) is a basic soil physical property which is essential for soil pore volume estimation and sediment source discrimination. The measurement of soil ρs is labor intensive and time-consuming. Pedotransfer functions (PTFs) have been developed for estimating ρs from readily available soil properties during the past decades. Existing PTFs are developed mainly based on soil datasets covering wide ranges of soil organic matter (SOM) contents. For soils from subtropical regions with low SOM values the accuracy of previous PTFs remains unknown. In this study we evaluated the performance of existing ρs PTFs by comparing model estimates to measurements of 175 soils from a subtropical region in China. The investigated soils had relatively low SOM contents (mostly<0.02 g g−1) and covered texture ranges from coarse sand to clayey soils. The Adams-based PTFs performed poorly, while the modified Adams PTFs and several simple linear or multiple regression PTFs produced relatively accurate ρs estimates for the 175 soils with root mean square errors (RMSEs) around 0.05 g cm−3 and mean biases within ± 0.03 g cm−3. Further multiple regressions indicated that the ρs of subtropical soils was simply a negative linear function of clay content. Despite conflicting several early reports, an independent dataset showed that the proposed linear model provided accurate ρs estimates for soils with low SOM contents from subtropical regions with a RMSE of 0.030 g cm−3 and mean bias of −0.013 g cm−3.

Effect of water conditions and nitrogen application on maize growth, carbon accumulation and metabolism of maize plant in subtropical regions

ABSTRACT Drought, water, and nitrogen (N) losses have always been great challenges for agricultural production in subtropical regions of China. To study appropriate irrigation regimes and reasonable N applications, a field experiment was conducted for summer maize (Zea mays L.) from 2018 to 2019. Two irrigation treatments, namely, rain-fed irrigation and supplementary irrigation, were designed, and five levels of N fertilizer were applied. The differences in the growth periods of biomass, leaf area index, agronomic traits, carbon accumulation, and carbon metabolism enzyme activity were measured. Findings revealed that the interaction of water and N has a significant impact on maize growth. Compared to other N treatments, N250 produced significantly higher biomass, leaf area index, agronomic traits, carbon accumulation, and carbon metabolism enzyme activity. In 2018, the agronomic traits and leaf area index were significantly higher than in 2019. Meanwhile, additional irrigation could help improve agronomic traits and the leaf area index. Further correlation analysis revealed that carbon accumulation was positively correlated with carbon metabolism enzyme activity, although lower at maturity than in the flowering period. Overall, the findings suggest that supplementary irrigation in conjunction with N250 treatment is a worthwhile measure for sustainable maize production in subtropical regions of China.

Irrigation and Nitrogen Fertilization Alter Soil Bacterial Communities, Soil Enzyme Activities, and Nutrient Availability in Maize Crop.

Irrigation and nitrogen (N) fertilization rates are widely used to increase crop growth and yield and promote the sustainable production of the maize crop. However, our understanding of irrigation and N fertilization in the soil microenvironment is still evolving, and further research on soil bacterial communities under maize crop with irrigation and N management in subtropical regions of China is needed. Therefore, we evaluated the responses of two irrigation levels (low and high irrigation water with 60 and 80% field capacity, respectively) and five N fertilization rates [i.e., control (N0), N200 (200 kg N ha−1), N250 (250 kg N ha−1), N300 (300 kg N ha−1), and N350 (350 kg N ha−1)] on soil bacterial communities, richness, and diversity. We found that both irrigation and N fertilization significantly affected bacterial richness, diversity index, and number of sequences. Low irrigation with N300 treatment has significantly higher soil enzymes activities, soil nutrient content, and bacterial alpha and beta diversity than high irrigation. In addition, the Proteobacteria, Actinobacteriota, Chloroflexi, and Firmicutes were the dominant bacterial phyla under both irrigation regimes. The acidic phosphates, acidic invertase, β-glucosidase, catalase, cellulase, and urease were positively correlated with the Shannon index under both low and high irrigation. Therefore, low irrigation improves soil nutrient utilization by boosting soil enzyme activity, directly affecting soil bacterial communities. It was concluded that greater soil nutrients, enzyme activities with higher bacterial diversity are the main indicators of soil reactivity to low irrigation water and N300 for maintaining soil fertility and soil microbial community balance.

Unlocking the Changes of Phyllosphere Fungal Communities of Fishscale Bamboo (Phyllostachys heteroclada) under Rhombic-Spot Disease Stressed Conditions

As an important nonwood bioresource, fishscale bamboo (Phyllostachys heteroclada Oliver) is widely distributed in the subtropical region of China. Rhombic-spot disease, caused by Neostagonosporella sichuanensis, is one of the most serious diseases that threatens fishscale bamboo health. However, there is limited knowledge about how rhombic-spot disease influences the diversity and structures of phyllosphere fungal communities. In this study, we investigated the phyllosphere fungal communities from stems, branches, and leaves of fishscale bamboo during a rhombic-spot disease outbreak using 18S rRNA sequencing. We found that only the phyllosphere fungal community from stems was significantly affected by pathogen invasion in terms of community richness, diversity, and structure. FUNGuild analysis revealed that the major classifications of phyllosphere fungi based on trophic modes in stems, branches, and leaves changed from symbiotroph-pathotroph, no obvious dominant trophic mode, and symbiotroph to saprotroph, saprotroph–pathotroph–symbiotroph, and saprotroph–symbiotroph, respectively, after pathogen invasion. The fungal community composition of the three tissues displayed significant differences at the genus level between healthy and diseased plants. The associations among fungal species in diseased samples showed more complex co-occurrence network structures than those of healthy samples. Taken together, our results highlight the importance of plant pathological conditions for the assembly of phyllosphere fungal communities in different tissues.

Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China

It is of great significance to explore the effects of different tillage practices on total nitrogen and its components in rice-wheat rotation farmland. The experiment was carried out in Jiangyan County, Jiangsu Province of China, and a total of four treatments were set up: minimum tillage (MT), rotary tillage (RT), conventional tillage (CT), and conventional tillage without straw retention (CT0). The total nitrogen (TN), light fraction nitrogen (LFN), heavy fraction nitrogen (HFN), particulate nitrogen (PN), and mineral-associated nitrogen (MN) in 0-20 cm soil were determined. The results show that MT increased TN concentration by2.26%-27.57% compared with the other treatments in 0-5 cm soil, but it lost this advantage in 5-10 cm and 10-20 cm soil. MT altered the concentration of LFN by 6.03%-95.86%, of HFN by 1.68%-20.75%, of PN by 12.58%-96.83%, and of MN by −1.73%-9.83% as compared to RT, CT, and CT0 in 0-5 cm soil, respectively. With the deepened of soil depth, the concentration of TN, LFN, HFN, PN, and MN decreased quickly in MT, which was lower than that in RT and CT at 10-20 cm soil depth. Straw return increased the concentration of TN and its components in 0-20 cm soil. The concentration of TN was extremely significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01). The variation of TN was significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01), and LFN showed the highest sensitivity to tillage practice. In general, minimum tillage combined with straw retention increased the concentration of soil TN and its components in topsoil. LFN was the best indicator to indicate the change in soil total nitrogen affected by tillage practice. Keywords: rice-wheat rotation, soil active nitrogen components, light fraction nitrogen, heavy fraction nitrogen, particulate nitrogen, mineral-associated nitrogen DOI: 10.25165/j.ijabe.20221503.5661 Citation: Cui S Y, Zhu X K, Cao G Q. Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China. Int J Agric & Biol Eng, 2022; 15(3): 146–152.