grong Chen

Effects of afforestation on phosphorus dynamics and biological properties in a New Zealand grassland soil.

Selected chemical, biochemical and biological properties of mineral soil (0–30 cm) were measured under a 19 year old forest stand (mixture of Pinus ponderosa and Pinus nigra) and adjacent unimproved grassland at a site in South Island, New Zealand. The effects of afforestation on soil properties were confined to the 0–10 cm layer, which reflected the distribution of fine roots (< 2 mm) in the soil profile. Concentrations of organic C, total N and P and all organic forms of P were lower under the forest stand, while concentrations of inorganic P were higher under forest compared with grassland, supporting the previously described suggestion that afforestation may promote mineralisation of soil organic matter and organic P. On the other hand, microbial biomass C and P, soil respiration and phosphatase enzyme activity were currently all lower and the metabolic quotient was higher in soil under forest compared with grassland, which is inconsistent with increased mineralisation in the forest soil. Reduced biological fertility by afforestation may be mainly attributed to changes in the quantity, quality and distribution of organic matter, and reduction in pH of the forest soil compared with the grassland soil. We hypothesize that the lower levels of C, N and organic P found in soil under forest are due to enhanced microbial and phosphatase activity during the earlier stages of forest development. Forest floor material (L and F layer) contained large amounts of C, N and P, together with high levels of microbial and phosphatase enzyme activity. Thus, the forest floor may be an important source of nutrients for plant growth and balance the apparent reduction in C, N and P in mineral soil through mineralisation and plant uptake.

The Australian three-dimensional soil grid: Australia’s contribution to the GlobalSoilMap project

Information on the geographic variation in soil has traditionally been presented in polygon (choropleth) maps at coarse scales. Now scientists, planners, managers and politicians want quantitative information on the variation and functioning of soil at finer resolutions; they want it to plan better land use for agriculture, water supply and the mitigation of climate change land degradation and desertification. The GlobalSoilMap project aims to produce a grid of soil attributes at a fine spatial resolution (approximately 100 m), and at six depths, for the purpose. This paper describes the three-dimensional spatial modelling used to produce the Australian soil grid, which consists of Australia-wide soil attribute maps. The modelling combines historical soil data plus estimates derived from visible and infrared soil spectra. Together they provide a good coverage of data across Australia. The soil attributes so far include sand, silt and clay contents, bulk density, available water capacity, organic carbon, pH, effective cation exchange capacity, total phosphorus and total nitrogen. The data on these attributes were harmonised to six depth layers, namely 0–0.05 m, 0.05–0.15 m, 0.15–0.30 m, 0.30–0.60 m, 0.60–1.00 m and 1.00–2.00 m, and the resulting values were incorporated simultaneously in the models. The modelling itself combined the bootstrap, a decision tree with piecewise regression on environmental variables and geostatistical modelling of residuals. At each layer, values of the soil attributes were predicted at the nodes of a 3 arcsecond (approximately 90 m) grid and mapped together with their uncertainties. The assessment statistics for each attribute mapped show that the models explained between 30% and 70% of their total variation. The outcomes are illustrated with maps of sand, silt and clay contents and their uncertainties. The Australian three-dimensional soil maps fill a significant gap in the availability of quantitative soil information in Australia.

Abundance and community structure of ammonia oxidizing bacteria and archaea in a Sweden boreal forest soil under 19-year fertilization and 12-year warming

PurposeBoreal forests are considered to be more sensitive to global climate change compared with other terrestrial ecosystems, but the long-term impact of climate change and forest management on soil microbial functional diversity is not well understood. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are the most important players in nitrogen (N) cycling-associated processes in terrestrial ecosystems. This study investigated the separate and combined impacts of long-term soil warming and fertilization on soil AOB and AOA community structures and abundances in a Norway spruce stand in northern Sweden.Materials and methodsThe soil-warming experiment was established in the buffer zones of two irrigated plots (I) and complete nutrient solution plots (IL) since 1995. The warming treatment started in April each year by maintaining soil temperature on warmed plots at 5°C above the temperature in unwarmed plots using heating cables. In August 2006, soil samples were collected from eight subplots for molecular analysis. The abundance of bacterial and archaeal amoA genes was determined by quantitative polymerase chain reaction. Similarly, total bacterial and archaeal population sizes have also been determined. The diversity of AOB and AOA was assessed by constructing amoA gene clone libraries, and different genotypes were screened with restriction fragment length polymorphism.Results and discussionResults showed that fertilization did not significantly affect the abundance of the bacterial amoA gene under either warming or non-warming conditions; however, warming decreased the abundance under fertilization treatments. No significant effects of fertilization and soil warming were observed on the number of thaumarchaeal amoA gene copies across all treatments. In this study, amoA gene abundance of AOB was significantly higher than that of AOA across all treatments. The community structure of both AOB and AOA was strongly influenced by fertilization. For bacterial amoA genes, Nitrosospira cluster 2 was present across all treatments, but the only genotype was observed in the fertilization treatments while, for thaumarchaeal amoA genes, the relative abundance of soil cluster 5 increased in fertilization treatments. By comparison, soil-warming effects on AOB and AOA community structure were not significant. Canonical correspondence analysis showed a positive correlation between fertilization and both dominant genotypes of AOB and AOA.ConclusionsThese results indicated that the abundance of AOA and AOB was not affected by fertilization or warming alone, but the interaction of fertilization and warming reduced the abundance of AOB. The community composition of ammonia-oxidizers was more affected by the nutrient-optimized fertilization than the soil warming.

Soil and Landscape Grid of Australia

The Soil and Landscape Grid of Australia (SLGA) is the first continental version of the GlobalSoilMap concept and the first nationally consistent, fine spatial resolution set of continuous soil attributes with Australia-wide coverage. The SLGA relies on digital soil mapping methods and integrates historical soil data, new measurement with spectroscopic sensors, novel spatial modelling and a web-service delivery architecture. The SLGA provides soil, regolith and landscape estimates at the centre point of 3 arcsecond grid cells (~90 × 90 m) across Australia. At each point, there are estimates of 11 soil attributes and confidence intervals for each estimate to a depth of 2 m or less, depth of regolith and a set of terrain descriptors. The information system also includes a library of mid-infrared spectra, an inference engine that allows estimation of additional soil parameters and an information model that enables users to access the system via web services. The explicit mapping of depth, bulk density and coarse fragments allows estimation of material stores and fluxes on a volumetric basis. The SLGA therefore has immediate applications in carbon, nitrogen and water process modelling. The map of regolith depth will find immediate application to studies of vadose zone processes, including solute transport, groundwater and nutrient fluxes beyond the root zone. Landscape attributes at 1 and 3 arcseconds are useful for a wide spectrum of ecological, hydrological and broader environmental applications. The SLGA can be accessed at no cost from www.csiro.au/soil-and-landscape-grid. It is managed and delivered as part of the Australian Soil Resource Information System (ASRIS).

Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils

Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine.

Effects of plant species on phosphorus availability in a range of grassland soils

Vegetative conversion from grass to forest may influence soil nutrient dynamics and availability. A short-term (40 weeks) glasshouse experiment was carried out to investigate the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil phosphorus (P) availability in 15 grassland soils collected across New Zealand using 33P isotopic exchange kinetics (IEK) and chemical extraction methods. Results from this study showed that radiata pine took up more P (4.5–33.5 mg P pot−1) than ryegrass (1.1–15.6 mg pot−1) from the soil except in the Temuka soil in which the level of available P (e.g., E1min Pi, bicarbonate extractable Pi) was very high. Radiata pine tended to be better able to access different forms of soil P, compared with ryegrass. There were no significant differences in the level of water soluble P (Cp, intensity factor) between soils under ryegrass and radiata pine, but the levels of Cp were generally lower compared with original soils due to plant uptake. The growth of both ryegrass and radiata pine resulted in the redistribution of soil P from the slowly exchangeable Pi pool (E> 10m Pi, reduced by 31.8% on the average) to the rapidly exchangeable Pi (E1min-1d Pi, E1d-10m Pi) pools in most soils. The values of R/r1 (the capacity factor) were also generally greater in most soils under radiata pine compared with ryegrass. Specific P mineralisation rates were significantly greater for soils under radiata pine (8.4–21.9%) compared with ryegrass (0.5–10.8%), indicating that the growth of radiata pine enhanced mineralisation of soil organic P. This may partly be ascribed to greater root phosphatase activity for radiata pine than for ryegrass. Plant species × soil type interactions for most soil variables measured indicate that the impacts of plant species on soil P dynamics was strongly influenced by soil properties.

Mineralisation of soil orthophosphate monoesters under pine seedlings and ryegrass

The effects of radiata pine (Pinus radiata D. Don) seedlings and ryegrass (Lolium perenne L.) on the mineralisation of orthophosphate monoesters in 7 grassland soils were assessed in a 10-month pot trial using NaOH–EDTA extraction and solution 31P NMR spectroscopy. Extraction with NaOH–EDTA recovered 46–86% of the total soil P, and NaOH–EDTA-extractable organic P determined by molybdate colourimetry ranged between 194 and 715 mg/kg soil, representing 34–85% of the total soil organic P. Orthophosphate monoesters were the predominant species of the extracted organic P in all soils, with much smaller concentrations of orthophosphate diesters, and traces of phosphonates. Concentrations of orthophosphate monoesters were consistently lower in soils under pine (103–480 mg P/kg soil) compared with the initial soils (142–598 mg P/kg soil) and most soils under grass (122–679 mg/kg soil). Mineralisation of myo-inositol hexakisphosphate accounted for 18–100% of the total mineralisation of orthophosphate monoesters in most soils under radiata pine. This suggests that supposedly recalcitrant inositol phosphates are available for uptake by radiata pine, although the extent of this varies among soils.

Warming and increased precipitation have differential effects on soil extracellular enzyme activities in a temperate grassland.

Few studies have conducted the responses of soil extracellular enzyme activities (EEA) to climate change, especially over the long term. In this study, we investigated the six-year responses of soil EEA to warming and increased precipitation in a temperate grassland of northern China at two depths of 0-10 and 10-20 cm. These extracellular enzymes included carbon-acquisition enzymes (β-glucosidase, BG), nitrogen-acquisition enzymes (N-acetylglucosaminidase, NAG; Leucine aminopeptidase, LAP) and phosphorus-acquisition enzymes (acid and alkaline phosphatases). The results showed that warming significantly increased acid phosphatase at the 0-10 cm depth and NAG at the 10-20 cm depth, but dramatically decreased BG and acid phosphatase in the subsurface. In contrast, increased precipitation significantly increased NAG, LAP and alkaline phosphatase in the surface and NAG, LAP and acid phosphatase in the subsurface. There was a significant warming and increased precipitation interaction on BG in the subsurface. Redundancy analysis indicated that the patterns of EEA were mainly driven by soil pH and NH(4)(+)-N and NO(3)(-)-N in the surface, while by NH(4)(+)-N and microbial biomass in the subsurface. Our results suggested that soil EEA responded differentially to warming and increased precipitation at two depths in this region, which may have implications for carbon and nutrient cycling under climate change.

Characterization of phosphorus availability in selected New Zealand grassland soils

Appropriate evaluation of phosphorus (P) availability in soil is aprerequisite for ensuring the productivity and long-term sustainable managementof agroecosystems. Fifteen soils presently under grassland were collected fromdifferent areas of New Zealand and soil P availability was assessed by isotopicexchange kinetics (IEK) and related to P forms obtained by chemicalfractionation (sequential extraction). Concentrations of total P determined inthe 15 soils ranged from 375 to 2607 mg kg−1(mean1104 mg kg−1). Mean concentrations of inorganic P(Pi) extracted by sequential extraction with ammonium chloride, sodiumbicarbonate, sodium hydroxide (first), hydrochloric acid and sodium hydroxide(second) were 1.2, 41, 205, 113 and 23 mg kg−1,respectively. Mean concentrations of organic P (Po) extracted by sodiumbicarbonate, sodium hydroxide (first) and sodium hydroxide (second) were 133,417 and 105 mg kg−1, respectively. Similarly,results from IEK analysis showed that the intensity (water soluble Pi (Cp)),capacity (R/r1 and n), and quantity (E value,isotopically exchangeable P pools (E1 min,E1 min–24 h,E24 h–3 m,E > 3 m)) factors varied markedlyamongst soils. Thus Cp concentrations ranged from 0.02–1.90 mgL−1, while concentrations of Pi determined in theE1 min, E1 min–24,E24 h–3 m,E>3 m pools were 2–29 (mean 10), 10–321(76), 11–745 (152), and 8–498 (177) mgkg−1, respectively. The corresponding values forR/r1 and n were 1.0–17.7 (mean 4.5) and0.10–0.50 (mean 0.37), respectively. Regression analysis revealed that Cpconcentrations were exponentially and inversely proportional toR/r1,n and P sorption index (PSI)(R2 = 0.806(P < 0.01), 0.852 (P < 0.01) and 0.660(P < 0.01), respectively). Cluster analysis identified twobroad groups of soils, namely those with low P availability (mean Cp0.11 mg L−1, E1 min Pi 5mg kg−1, R/r1 3.9,n 0.44), and those with high P availability (mean Cp 1.33mg L−1, E1 min Pi 20mg kg−1, R/r1 1.21,n 0.16). Correlation analysis indicated thatE1 min P i was significantly correlated with bicarbonateextractable Pi (BPi, R2 = 0.37,P < 0.05) and thesum of ammonium chloride extractable Pi (APi) and BPi(R2 = 0.38,P < 0.05). However, the concentration of Pi in theE1 min pool was generally lower than the sum of APi andBPi. Sodium hydroxide extractable Pi (N1Pi) was significantlycorrelated with the sum of the E1 min,E1 min–24 h,E24 h–3 m Pi pools(R2 = 0.974, P < 0.01),indicating that N1Pi fractioncould be considered as representing potentially available soil P for pasturespecies over a growing season.

The Spatial Factor, Rather than Elevated CO2, Controls the Soil Bacterial Community in a Temperate Forest Ecosystem

ABSTRACT The global atmospheric carbon dioxide (CO2) concentration is expected to increase continuously over the next century. However, little is known about the responses of soil bacterial communities to elevated CO2 in terrestrial ecosystems. This study aimed to partition the relative influences of CO2, nitrogen (N), and the spatial factor (different sampling plots) on soil bacterial communities at the free-air CO2 enrichment research site in Duke Forest, North Carolina, by two independent techniques: an entirely sequencing-based approach and denaturing gradient gel electrophoresis. Multivariate regression tree analysis demonstrated that the spatial factor could explain more than 70% of the variation in soil bacterial diversity and 20% of the variation in community structure, while CO2 or N treatment explains less than 3% of the variation. For the effects of soil environmental heterogeneity, the diversity estimates were distinguished mainly by the total soil N and C/N ratio. Bacterial diversity estimates were positively correlated with total soil N and negatively correlated with C/N ratio. There was no correlation between the overall bacterial community structures and the soil properties investigated. This study contributes to the information about the effects of elevated CO2 and soil fertility on soil bacterial communities and the environmental factors shaping the distribution patterns of bacterial community diversity and structure in temperate forest soils.