Irrigation is in the spotlight of land-use planning in semi-arid and sub-humid regions. It can be a promising practice to promote soil organic C storage (SOC), although it may also involve an ...increase in soil GHG emissions. Assessing the impact of its adoption on SOC storage is crucial to better understand its potential role in terms of agricultural sustainability and climate policies. In this study, we measured and modeled the changes in soil organic C storage and dynamics in the tilled soil layer (0–30 cm) of an experimental field on a calcareous soil with two different crops (maize, a C4 plant, and wheat, a C3 plant), cultivated with and without irrigation for 7 years. We hypothesized that changes in SOC storage occur when introducing irrigation and/or different crops in an agrosystem, and that they would be related to changes in the incorporation of crop residues, their partitioning between the labile and the stable fraction, and C losses by mineralization. Our results validated theses hypotheses only partially. Over the 7-year study period, irrigation significantly increased total (TOC) and sand-size (50–2,000 μm) particulate organic C (POC
50−2,000
) stocks in the tilled layer (0–30 cm): +7.1% TOC and +12.1% POC
50−2,000
for maize, and +7.0 and +12.3% for wheat. A parallel two-pool SOC model based on TOC and POC
50−2,000
fractions and the C3-C4 plant shift allowed understanding that the observed changes in SOC storage were most likely related to an increase in C inputs from crop residues, and to a more efficient incorporation of these residues with irrigation. The mean residence time of SOC in the two modeled pools did not allow to support our hypothesis of changes in SOC mineralization with irrigation. The limitations of SOC fractionation, which implied that some labile fractions might have been lost from POC
50−2,000
and recovered in the fraction identified as slow-turning, together with the interaction of the carbonate-rich mineral phase of this soil can explain at least partially this observation. We conclude that irrigation can contribute to effectively increase SOC storage in the mid-term, but its effect might be dependent upon the type of crops and soil.
Higher exportation of harvest residues from forests due to increased demand for woody biomass, has reportedly diminished soil mineral resources and may lead to degraded tree nutrition as well as ...growth. However, as nutrients become less available in the soil, the remobilization of nutrients in biomass tissues (plant internal cycling) helps sustain tree nutrition. Our study aims to quantify the impact of Removing Harvest Residues and Litter (RHRL) during five years on tree growth, wood density, and stem wood nutrient concentrations in young beech and oak forest stands.
Our study found that, RHRL significantly decreased tree growth ring width by 14%, and wood density by 3%, in beech trees, in near bark rings. RHRL also significantly reduced nutrient concentration in near bark and near pith areas of both studied species. Mg, Na and S were found lower by 44%, 76%, and 56%, respectively, in near bark area of beech trees. In near bark area of oak trees, K, Ca, Mg, Na, S, and Fe were lower by 20%, 25%, 41%, 48%, 41%, and 16%, respectively. K and Mg concentrations decreased more strongly in near pith area compared to near bark area suggesting internal translocation of these two elements.
In beech trees, wood density proved to be an important factor while quantifying the effect of removing harvest residuals on tree growth and biomass. Soil nutrient loss intensified the remobilization of nutrients contained in older tree rings (close to the pith) towards newly formed rings (close to bark). In our study, in beech trees, K was found to be the most recycled major nutrient. These results demonstrate the potential of such analysis for providing valuable insight into the effect of RHRL in premature stands on the physiological adaptive strategies of trees and an indication of soil fertility status.
Purpose
Douglas-fir occupies a growing role in the European timber industries but its effects on soils and the environment are still not well understood. We monitored the biogeochemical cycle of ...major elements in 11 representative mature stands throughout France over the 2013 to 2020 period to better understand repercussions on soil processes.
Methods
The present study is focused on throughfall and soil solution chemistry: concentrations were measured monthly at 15 cm and 60 cm depth and fluxes of major anions and cations were computed.
Results
Our results show that nitrate strongly dominated the soil solution chemistry: concentrations were elevated (>20 mg L
−1
) for 8 out of 11 sites with mean annual NO
3
−
values ranging from 2 to 253 mg L
−1
. Fluxes of nitrate at 60 cm of depth, ranging from 23 to 309 kg ha
−1
yr
−1
, were much higher than those in throughfall for nine studied sites. Nitrate, which was the dominant anion in soil solution, associated either to Ca
2+
, Mg
2+
and K
+
, or to Al
3+
was lost out of the soil-plant system through leaching.
Conclusions
These results suggest a production of NO
3
−
in the soil exceeding tree uptake and microbial immobilization resulting in strong ongoing soil acidification at many sites and potential degradation of water quality. Significant negative correlations were found between nitrate concentration in soil solution and sandy texture, soil C and N, site elevation and, annual rainfall, but further research is necessary to clarify the role of these factors in reducing the negative impacts on terrestrial and aquatic ecosystems.
In rural areas, nitrate concentrations in surface waters most often originate from the leaching of excess N fertilizer in agricultural lands, whereas forested catchments often have good water ...quality. However, Douglas-fir plantations may induce nitrogen cycle unbalances which may lead to an excess of nitrate production in the soil. We hypothesize that the excess of production of nitrate in the soil and nitrate leaching to streamwater is greater in catchments planted with Douglas fir. We used paired catchments in both France and Luxembourg with different land covers (Douglas-fir, Spruce, Deciduous, Grassland and clearcut) which were monitored over a 3–5 year period in order to assess the effect of Douglas-fir plantations on the chemical composition of surface water. Nitrate concentration in the soil and groundwater were also monitored. The results show that nitrate concentrations in streams draining Douglas-fir catchments were two to ten times higher than in streams draining other land covers, but were similar to the clearcut catchment. Nitrate concentrations under Douglas-fir in groundwater (up to 50 mg L−1) and in the soil were also higher than under all other land covers. Soil nitrate concentration was related to stream nitrate concentration. This suggests that soil processes, through excessive nitrate production under Douglas-fir, are driving the nitrate concentration in the stream water and our hypothesis of a transfer of a fairly large proportion of this excessive production from the soil to the stream is supported. This study also shows that nitrate concentrations in surface and ground waters in rural areas could also originate from Douglas fir forested catchments. The impact of Douglas-fir is nevertheless reduced downstream through a dilution effect: mixing tree species at the catchment scale could thus be a solution to mitigate the effect of Douglas-fir on nitrate concentration in surface waters.
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•Higher nitrate concentration in streams draining Douglas-fir than other covers•NO3- in surface waters can derived from forested catchments draining Douglas fir•Imbalance between production and consumption of NO3 revealed by a seasonal dynamics•Nitrate concentration in streams is linked to excessive soil nitrate production
•A unique dataset combining soil properties and stand productivity was compiled.•Common soil chemical properties were poor predictors of stand productivity.•Forest soils with low nutrient stocks ...sometimes exhibit high stand productivity.•Nutrient fluxes and cycling could better explain stand productivity.
Forest soil fertility can be defined as a combination of physical, chemical and biological factors characterising the biomass production capacity of the soil. However, numerous ecological variables affect tree growth and the aim of the present study was to investigate the specific influence of soil chemical properties on tree productivity at 49 acidic forest sites. A standardized tree productivity index based on tree height expressed as dominant height of the studied stand divided by maximum tree height observed at the same age for the same species in the same climatic region was firstly computed at each site. This index is assumed to limit the influence of species, ages and climate. A soil database was also compiled with data on soil properties from 47 temperate (France) and two tropical (Congo, Brazil) sites. Data included seven tree species, varying in age from 1 to 175 years. Commonly used indicators such as C:N ratio, soil pH, as well as available and total pools of soil nutrients were compared to the standardized tree productivity index, to find the most reliable indicator(s). Nutrient pools at fixed mineral soil depths (down to 100 cm) were used, as well as (for 11 stands) the depth comprising 95% of fine roots.
Our results show that none of the common soil chemical parameters tested in this paper could individually explain stand productivity. Combinations of different parameters were also tested using PCA and they could better explain the variability of the data set but without being able to separate the sites according to their standardized tree productivity index. Moreover, random Forests performed on our dataset were unable to properly predict the standardized tree productivity index. Our results reinforce the idea that the influence of the soil chemical fertility on stand productivity is complex and the soil chemical parameters alone (individually or combined) are poor predictors of tree productivity as assessed by the H0:Hmax index. In this paper we focused on static soil chemical indicator and more dynamic indictors, such as nutrient fluxes involved in the biogeochemical cycles, could better explain stand productivity. A companion paper (Legout et al., 2020) focuses on the connection between productivity and different components of the biogeochemical cycle, using data from 11 of the stands presented in this paper.
In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The ...pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging.
In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1molL−1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases.
Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil solution chemistry on very short-term time scales. These phases are very abundant in acid soils and, in the present study, represent a substantial calcium pool (equivalent in size to the Ca exchangeable pool). The gradual isotopic dilution of Mg and Ca isotope ratios in the leaching solution during the experiment evidenced an input flux of Mg and Ca originating from a pool other than the labile pool. While the Mg input flux originated primarily from the weathering of primary minerals and secondarily from the non-crystalline phases, the Ca input flux originated primarily from the non-crystalline phases. Our results also show that the net calcium release flux from these phases may represent a significant source of calcium in forest ecosystems and actively contribute to compensating the depletion of Ca exchangeable pools in the soil. Non-crystalline phases therefore should be taken into account when computing input-output nutrient budgets and soil acid neutralizing capacity.
In terrestrial ecosystem studies, water drainage and nutrient leaching in the soil profile are estimated with hydrological models. Comparing modeled results to empirical data or comparing data from ...different models is, however, difficult because the uncertainty of input–output budget predictions is often unknown. In this study, we developed a procedure combining a Generalized Likelihood Uncertainty Estimation and a Monte-Carlo modeling approach to estimate uncertainty in model parameter estimates and model outputs water drainage and nutrient leaching fluxes for the WatFor water balance model. This procedure was then applied to compare different model optimization strategies (daily soil moisture measurements, monthly measurements of chloride concentrations in soil solution, and the elution of a concentrated chloride) at the same experimental site in a 90-year-old European beech (Fagus sylvatica L.) forest in Brittany (France). We show that the monitoring data of natural variations of chloride concentrations in soil solution were the most efficient dataset to calibrate the WatFor model compared to the soil moisture and chloride tracing experimental data. We also show that water tracing experimental data are the most efficient data to estimate the preferential flow generation model parameters. The optimization strategy had little influence on the predicted water drainage flux and nutrient leaching flux at the root zone boundary on a yearly time scale but influenced water and nutrient fluxes in the topsoil layers.
•Five beech forest ecosystems were limed with carbonates 20 to 40 years ago.•Liming reduces acidity, improves soil fertility, tree nutrition and tree growth.•Biological cycling tends to maintain the ...applied elements in the soil-plant.•Liming with carbonate may cause long term nutrient imbalances in Mg and K.
Most forest ecosystems grow on acid and nutrient poor soils. In many cases, a slow degradation of forest soil chemical fertility due to increasing external pressures (decreasing atmospheric inputs, intensification of biomass harvesting and silvicultural practices) has been observed and is a growing concern in the international forest community. When the pressure endured by low fertility forest ecosystems is too intense, nutrient losses and ecosystem function losses may occur, forest decline being the ultimate stage of this process. In such cases, forest liming with a carbonate product is a solution to restore soil fertility and reduce soil acidity, globally improve the ecosystem functioning and compensate for nutrient losses caused by biomass harvest and exportation. However, the effects of liming on ecosystem processes and the biogeochemical cycling of nutrients in forest ecosystems are still unclear. We studied the dynamics of magnesium and calcium originating from the dissolution of liming products in the different compartments (organic and mineral soil layers and, aboveground biomass) of five long-term (20 to 40 years) monitoring beech (Fagus sylvatica L.) plots located in Northern France from ecosystem magnesium and calcium budgets.
Compared to the control plots, soil exchangeable pools of Mg and Ca in the 0–15 cm mineral soil layer increased during the first decade after liming but these differences rapidly decreased after 20–30 years. The effect of liming on foliar concentrations and tree growth was still observed after 40 years, most probably because the biological cycling of these elements was more dynamic in the limed plots. Liming increased the decomposition rate of the soil organic layer but the pools of Mg and Ca in this layer remained relatively stable over time, probably because Mg and Ca concentrations in foliage and litterfall increased after the liming. Liming effects varied between sites depending on the liming product and amount, and the initial chemical fertility level of the soil. Although liming operations may help improve forest soil fertility, they may also generate nutrient deficiencies and/or imbalances for nutrients that are poorly available in the soil. The planning of liming operations therefore necessitates a thorough soil chemical fertility diagnosis.
Nutrient limitation of tree growth can intensify when nutrients are lost to forest harvest, creating challenges for forest growth and sustainability. Forest harvest accelerates nutrient loss by ...removing nutrient-containing biomass and by increasing nutrient leaching, shaping patterns of nutrient depletion that cause long-term shifts in nutrient limitation. Nitrogen most frequently limits tree growth, but where nitrogen is abundant, nutrient limitation often shifts to phosphorus and base cations, depending on soil mineralogy. We used the process-based biogeochemical model NutsFor to evaluate how multiple elements can limit long-term forest growth via interactions between soil nitrogen (low vs. high nitrogen) and soil mineralogy (sedimentary vs. basaltic bedrock). Simulations were run for 525 years with 40-year harvest intervals for managed Douglas-fir forests of the Oregon Coast Range. In low nitrogen sites, nutrient limitation switched after several centuries from nitrogen to phosphorus, as cycles of forest growth and harvest depleted soil organic phosphorus pools. In contrast, high nitrogen sites displayed severe base cation depletion and reduced tree growth within only one to two rotations, with sedimentary bedrock sites limited by calcium and basaltic sites by both calcium and potassium. Harvesting stimulated the largest fractional losses of nitrogen and potassium across all simulations, and additionally of calcium in high nitrogen sites. These multi-element simulations of interactions among harvesting, soil nitrogen, and bedrock type provide a set of testable predictions to guide monitoring and changes in management aimed at sustaining long-term forest productivity across a wide range of soil biogeochemical conditions.
Forest ecosystems are often found on acid soils where calcium availability depends on two main inputs (atmospheric deposition and the weathering of soil minerals) and on the biological cycling of ...nutrients. In the context of global change (decreasing atmospheric inputs, increasing biomass exportation, climate change), it is important to determine calcium sources to the ecosystem and tree nutrition to better understand how forest ecosystems will respond to these changes over time. The aim of this study was to study and compare Ca pools and cycling in two mature forest ecosystems (Clermont en Argonne and Azerailles) developed on two contrasting polycyclic soils (Lorraine plateau, eastern France) and identify the Ca sources contributing to ecosystem functioning. At both sites, soil Ca pools were measured; atmospheric deposition of Ca was monitored from bulk precipitation and throughfall chemistry; Ca biological cycling was assessed by measuring litterfall and by a litter decomposition experiment; strontium (87Sr/86Sr) isotope data in the soil profile (fine roots, exchangeable pool, bulk soil) was used to estimate the distribution of Sr and Ca uptake in the soil profile and the relative contribution of mineral weathering in the soil layers to total ecosystems inputs. Despite important differences in Ca availability in the topsoil between both sites, tree growth and nutrition indicators showed no significant difference. This discrepancy is not explained by the biological cycling of Ca but may be partly explained by higher Ca deposition at the Ca-poorer site. Strontium isotope data enabled to show important differences of Ca sources for tree uptake. At the Ca-poorer site, deep soil layers (>105cm) potentially represent from 32% to 100% of total Sr uptake. At the Ca-richer site, results suggest that uptake is more evenly distributed in the soil profile. Sr isotope data coupled with a modeling approach suggest that two different mineral sources exist in the soil profile: a radiogenic Sr source in the topsoil (87Sr/86Sr>0.717) and a less radiogenic source in depth (87Sr/86Sr<0.717). The deep mineral source may represent from 40% to 86% of total Sr inputs at the poorer site and from 25% to 86% at the richer site. The origin of this deep strontium source is unclear but soil mineralogy suggests an allochthonous origin. We hypothesize that this deep source originates from capillary rise of the groundwater aquifer. This nutrient input to forest ecosystems is not commonly taken into account but may strongly participate in maintaining the chemical fertility of soils over time.
•Sr isotopes were used to trace Ca sources and cycles in two forest polycyclic soils.•Different available Ca pools were not reflected in tree growth and nutrition indicators.•Modeling and isotope data showed Sr uptake from deep soil layers.•Modeling and isotope data suggest two different sources of mineral weathering.•Groundwater aquifers may represent an important input to forest ecosystems.
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