Covariation between plant biodiversity and soil systems in a European beech forest and a black pine plantation:the case of Mount Faito,(Campania,Southern Italy)

Both climate and land-use changes,including the introduction and spread of allochthonous species,are forecast to affect forest ecosystems.Accordingly,forests will be affected in terms of species composition as well as their soil chemical and biological characteristics.The possible changes in both tree cover and soil system might impact the amount of carbon that is stored in living plants and dead biomass and within the soil itself.Additionally,such alterations can have a strong impact on the detrital food web that is linked to litter decomposition.Although there are studies on the infuence of plant diversity on soil physical and chemical characteristics,the effects on soil biological activity and carbon storage processes remain largely unknown.The aim of this study was to investigate and compare chemical and biological variables in covariation with plant communities in an autochthonous beech forest(Fagus sylvatica L.)and a black pine plantation(Pinus nigra J.F.Arnold subsp.nigra).Our results confirmed that the two communities were considerably different,with the old-growth beech community having a lower number of plant species and the pine community was in development as a consequence of anthropogenic activities.These aspects of the two communities were also refected in the soil,with the beech soil having higher nitrogen levels and a more specialized microbial community compared to the pine soil,with most extracellular enzymes(such as peroxidase and chitinase)showing lower activity in the pine soil.

Effects of grazing on carbon and nitrogen in plants and soils in a semiarid desert grassland,China

Grazing can modulate the feedback between vegetation and soil nutrient dynamics（carbon and nitrogen）,altering the cycles of these elements in grassland ecosystems.For clarifying the impact of grazing on the C and N in plants and soils in the desert grassland of Ningxia,China,we examined the plant biomass,SOC（soil organic carbon）,total soil N and stable isotope signatures of plants and soils from both the grazed and ungrazed sites.Significantly lower aboveground biomass,root biomass,litter biomass and vegetation coverage were found in the grazed site compared to the ungrazed site,with decreases of 42.0%,16.2%,59.4% and 30.0%,respectively.The effects of grazing on plant carbon,nitrogen,？15N and ？13C values were uniform among species.The levels of plant carbon and nitrogen in grasses were greater than those in the forbs（except for the carbon of Cynanchum komarovii and Euphorbia esula）.Root 15 N and 13 C values increased with grazing,while the responses of root carbon and nitrogen to grazing showed no consistent patterns.Root 15 N and 13 C were increased by 79.0% and 22.4% in the grazed site compared to the ungrazed site,respectively.The values of SOC and total N were significantly lower in the grazed than in the ungrazed sites for all sampling depths（0–10 and 10–20 cm）,and values of SOC and total N at the surface（0–10 cm） were lower than those in the deeper soils（10–20 cm）.Soil ？15N values were not affected by grazing at any sampling depth,whereas soil ？13C values were significantly affected by grazing and increased by 19.3% and 8.6% in the soils at 0–10 and 10–20 cm,respectively.The soil ？13C values（–8.3‰ to –6.7‰） were higher than those for roots（–20.2‰ to –15.6‰） and plant tissues（–27.9‰ to –13.3‰）.Our study suggests that grazing could greatly affect soil organic carbon and nitrogen in contrast to ungrazed grassland and that grazing appears to exert a negative effect on soil carbon and nitrogen in desert grassland.

Identification of candidate soil microbes responsible for small-scale heterogeneity in strawberry plant vigour

Studies were conducted to identify candidate soil microbes responsible for observed differences in strawberry vigour at a small spatial scale, which was not associated with visual disease symptoms. Samples were obtained from the soils close to the rhizosphere of ‘big＇ and ‘small＇ plants from small plots which exhibited large local heterogeneity in plant vigour. A metabarcoding approach was used to profile bacterial and fungal compositions, using two primer pairs for 16 S ribosomal RNA genes（16S r DNA） and one for the fungal internal transcribed spacer（ITS） region. Of the two 16 S r DNA primer sets, the 341F/805 R resulted in sequences of better quality. A total 28 operational taxonomic units（OTUs） had differential relative abundance between samples from ‘big＇ and ‘small＇ plants. However, plausible biological explanation was only possible for three fungal OTUs. Two were possible phytopathogens： Verticillium spp. and Alternaria alternata although the latter has never been considered as a main pathogen of strawberry in the UK. For samples from ‘small＇ plants, the abundance of these OTUs was much greater than from ‘big＇ plants. The opposite was true for a mycorrhizal OTU. These results suggest that soil microbes related to crop production can be identified using metabarcoding technique. Further research is needed to assess whether A. alternata and Verticillium spp. could affect strawberry growth in the field.

Changes in Soil Biota Resulting from Growth of the Invasive Weed, Ambrosia artemisiifolia L.(Compositae), Enhance Its Success and Reduce Growth of Co-Occurring Plants

Exotic plant invasion presents a serious threat to native ecosystem structure and function. Little is known about the role of soil microbial communities in facilitating or resisting the spread of invasive plants into native communities. The purpose of this research is to understand how the invasive annual plant Ambrosia artemisiifolia L. facilitates its competition capacity through changing the structure and function of soil microbial communities. The soil characteristics of different areas invaded by A. artemisiifolia were examined. Greenhouse experiments were designed to assess the effect of A. artemisiifolia invasion-induced changes of soil biota on co-occurring plant growth, and on the interactions between A. artemisiifolia and three co-occurring plant species. The results showed that the soil organic C content was the highest in heavily invaded sites, the lowest in native plant sites, and intermediate in newly invaded sites. Soil available N, P and K concentrations in heavily invaded site were 2.4, 1.9 and 1.7 times higher than those in native plant soil, respectively. Soil pH decreased as A. artemisiifolia invasion intensity increased, and was lower in invaded sites（heavily invaded and newly invaded） than in native plant sites. The soil microbial community structure was clearly separated in the three types of sites, and A. artemisiifolia invasion increased anaerobe, sulfate-reducing bacteria and actinomycete abundance. Soil biota of invaded sites inhibits growth of co-occurring plants（Galinsoga parvifloraCav., Medicago sativa L. and Setaria plicata（Lam.） T. Cooke.） compared to soil biota from un-invaded sites, but facilitates A. artemisiifolia growth and competition with co-occurring plants. A. artemisiifolia biomass was 50-130% greater when competing with three co-occurring plants, compared to single-species competition only（invasion by A. artemisiifolia alone）, in heavily invaded soil. Results of the present study indicated that A. artemisiifolia invasion alters the soil microbial community in a way that favors itself while inhibiting native plant species, with measurable effects on performance of co-occurring plants.

Response of plant physiological parameters to soil water availability during prolonged drought is affected by soil texture

Soil water deficit is increasingly threatening the sustainable vegetation restoration and ecological construction on the Loess Plateau of China due to the climate warming and human activities.To determine the response thresholds of Amygdalus pedunculata(AP)and Salix psammophila(SP)to soil water availability under different textural soils,we measured the changes in net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),leaf water potential(ψw),water use efficiency(WUE)and daily transpiration rate(Td)of the two plant species during soil water content(SWC)decreased from 100%field capacity(FC)to 20%FC in the sandy and loamy soils on the Loess Plateau in the growing season from June to August in 2018.Results showed that Pn,Gs,WUE and Td of AP and SP remained relatively constant at the beginning of soil water deficit but decreased rapidly as plant available soil water content(PASWC)fell below the threshold values in both the sandy and loamy soils.The PASWC thresholds corresponding to Pn,Gs and Ci of AP in the loamy soil(0.61,0.62 and 0.70,respectively)were lower than those in the sandy soil(0.70,0.63 and 0.75,respectively),whereas the PASWC thresholds corresponding to Pn,Gs and Ci of SP in the loamy soil(0.63,0.68 and 0.78,respectively)were higher than those in the sandy soil(0.58,0.62 and 0.66,respectively).In addition,the PASWC thresholds in relation to Td and WUE of AP(0.60 and 0.58,respectively)and SP(0.62 and 0.60,respectively)in the loamy soil were higher than the corresponding PASWC thresholds of AP(0.58 and 0.52,respectively)and SP(0.55 and 0.56,respectively)in the sandy soil.Furthermore,the PASWC thresholds for the instantaneous gas exchange parameters(e.g.,Pn and Gs)at the transient scale were higher than the thresholds for the parameters(e.g.,Td)at the daily scale.Our study demonstrates that different plant species and/or different physiological parameters exhibit different thresholds of PASWC and that the thresholds are affected by soil texture.The result can provide guidance for the rational allocation and sustainable management of reforestation species under different soil conditions in the loess regions.

Spatial variations of Pb in the vertical zone of the soil-plant system in the Changbai Mountain National Nature Reserve

The characteristics of vertical and horizontal variations of lead element(Pb) in soil plant system of vertical zone in Changbai Mountain National Nature Reserve(CNNR) were studied. The results showed that Pb concentrations in soils of vertical zone are all above 25 mg/kg, and the average Pb concentration of each soil zone negatively correlates its degree of variation, i.e. brown coniferous forest soil zone has the lowest average Pb concentration of four soil zones, and the highest horizontal variation; however, mountain soddy forest soil has the highest average Pb concentration, and the lowest horizontal variation; the average concentration of plant Pb of each plant zone is lower than the worldwide average level of Pb in plant(Clarke), respectively, and plant Pb content order is consistent with soil Pb content order, but their horizontal variations are different from those in soil zones, the variation of mountain tundra forest zone is highest, but Betula ermanii forest zone the lowest. Vertical variation of plant Pb is obviously higher than that in soils with variation coefficient of 89.76%; the enrichment capability of plant for Pb is depended on the plant types and the different organs of plant; parent material and parent rock, pH values, soil organic matter and soil particle fraction etc. are the main factors influencing variations of Pb content in soil plant system of vertical zone in CNNR.

Response of nitrogen fractions in the rhizosphere and bulk soil to organic mulching in an urban forest plantation

Nitrogen is an essential component in forest ecosystem nutrient cycling.Nitrogen fractions,such as dissolved nitrogen,ammonium,nitrate,and microbial biomass nitrogen,are sensitive indicators of soil nitrogen pools which affect soil fertility and nutrient cycling.However,the responses of nitrogen fractions in forest soils to organic mulching are less well understood.The rhizosphere is an important micro-region that must be considered to better understand element cycling between plants and the soil.A field investigation was carried out on the effect of mulching soil in a 15-year-old Ligustrum lucidum urban plantation.Changes in total nitrogen and nitrogen fractions in rhizosphere and bulk soil in the topsoil(upper 20 cm)and in the subsoil(20-40 cm)were evaluated following different levels of mulching,in addition to nitrogen contents in fine roots,leaves,and organic mulch.The relationships between nitrogen fractions and other measured variables were analysed.Organic mulching had no significant effect on most nitrogen fractions except for the rhizosphere microbial biomass nitrogen(MBN),and the thinnest(5 cm)mulching layer showed greater effects than other treatments.Rhizosphere MBN was more sensitive to mulching compared to bulk soil,and was more affected by soil environmental changes.Season and soil depth had more pronounced effects on nitrogen fractions than mulching.Total nitrogen and dissolved nitrogen were correlated to soil phosphorus,whereas other nitrogen fractions were strongly affected by soil physical properties(temperature,water content,bulk density).Mulching also decreased leaf nitrogen content,which was more related to soil nitrogen fractions(except for MBN)than nitrogen contents in either fine roots or organic mulch.Frequent applications of small quantities of organic mulch contribute to nitrogen transformation and utilization in urban forests.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Chihuahuan Desert Soil Biota

Deserts have traditionally been considered as a low moisture system where biological activity is triggered by unpredictable rainfall in time and space. Studies on desert ecosystems functions, processes, dynamics and diversity of soil biota had been found to contribute to understanding of their role in primary production and management of soil ecosystems. As belowground biota is very diverse they are playing an important role in above as well below ground essential ecosystem processes e.g. primary production, decomposition, nutrient mineralization etc. The challenge is to use the emerging knowledge of soil biota diversity in understanding basic ecosystems function.

Agronomic Practices and Macronutrients Status of Different Age Groups of Smallholder Oil Palm (Elaeis guineensis Jacq.) Plantations in Dibombari Sub-Division, Cameroon

Oil palm is cultivated by agro-industries and smallholders for vegetable oil production. Good farm management practices with balanced soil and plant macronutrients are needed to attain optimum yields. Smallholder oil palm farmers of Dibombari Sub-Division, Cameroon, suffer from low on farm yields which could emanate from the agronomic practices implemented, which also has an influence on the soil and plant macronutrient status. This study provides information on the agronomic practices, soil and plant macronutrients status in smallholder oil palm fields. Structured questionnaires were administered to 200 farmers to collect data on their agronomic practices, using a stratified random sampling design. Soil and plants were sampled from plantations of different age groups (control, >0 - 4 years, >4 - 8 years and >8 - 15 years’ plantations) in four locations of the Sub-Division (i.e. Dibombari-central, Bonamateke, Bomono and Nkapa) using a randomized complete block design. Data collected, was analyzed using descriptive and inferential statistics. The results showed that 65% of farmers planted Tenera variety, with majority of them below the standards for weeding (81%), fertilizer use (100%), pruning (62%), pest/disease control (90.5%) and harvesting (96%) practices. Soil macronutrients were low across the different plantations except P which was optimal at >0 - 4 years and >4 - 8 years’ plantations but low at >8 - 15 years’ plantation. Similarly, for plant macronutrients, N and P were optimal across the different plantations, while K and Mg were optimal at >0 - 4 years’ plantation but low at >4 - 8 years and >8 - 15 years’ plantations. Thus, agronomic practices and macronutrient status of soil and plants were below standards in smallholder oil palm plantations of Dibombari, leading to low yields of fresh fruit bunches.

Growth and nutrient accumulation of Brazil nut trees(Bertholletia excelsa) in agroforestry at different fertilizer levels

The Brazil nut tree（Bertholletia excelsa） is a frequent component of agroforestry systems in the Amazon because of its adaptation to nutrient-poor upland soils and multiple uses.We investigated the aboveground biomass production（kg dry weight）,nutrient uptake and requirements（N,P,Ca,Mg,K） of Brazil nut trees of different sizes grown under agroforestry conditions and fertilized at different levels.Eight of 70 experimental trees with different size were harvested and stem,branches and leaves were separated.Nutrient contents were determined for three trees of varying size.Average tree growth was fast,but variability was high,suggesting considerable potential for the improvement of this economically important species.The trees responded to increased levels of fertilizer and lime with significantly increased foliar nutrient contents and growth,probably because of the improved availability of Mg and Ca for which the species seems to have a relatively high demand.In contrast to Brazil nut trees grown in forest or dense plantations,the agroforestry trees invested a substantial part of their biomass and nutrients in large branches and developed spreading crowns.To improve stem form,reduce competition with associated crops for light and recycle nutrients,regular pruning of lower branches or planting arrangements that favor self-pruning are recommended.These measures would also increase the recycling of Ca and Mg,large quantities of which are contained in the branches.

Nondestructive estimation of bok choy nitrogen status with an active canopy sensor in comparison to a chlorophyll meter

Precise estimation of vegetable nitrogen(N)status is critical in optimizing N fertilization management.However,nondestructive and accurate N diagnostic methods for vegetables are relatively scarce.In our two-year field experiment,we evaluated whether an active canopy sensor(GreenSeeker)could be used to nondestructively predict N status of bok choy(Brassica rapa subsp.chinensis)compared with a chlorophyll meter.Results showed that the normalized difference vegetation index(NDVI)and ratio vegetation index(RVI)generated by the active canopy sensor were well correlated with the aboveground biomass(AGB)(r=0.698–0.967),plant N uptake(PNU)(r=0.642–0.951),and root to shoot ratio(RTS)(r=-0.426 to-0.845).Compared with the chlorophyll meter,the active canopy sensor displayed much higher accuracy(5.0%–177.4%higher)in predicting AGB and PNU and equal or slightly worse(0.54–1.82 times that of the chlorophyll meter)for RTS.The sensor-based NDVI model performed equally well in estimating AGB(R2=0.63)and PNU(R2=0.61),but the meter-based model predicted RTS better(R2=0.50).Inclusion of the days after transplanting(DAT)significantly improved the accuracy of sensor-based AGB(19.0%–56.7%higher)and PNU(24.6%–84.6%higher)estimation models.These findings suggest that the active canopy sensor has a great potential for nondestructively estimating N status of bok choy accurately and thus for better N recommendations,especially with inclusion of DAT,and could be applied to more vegetables with some verification.