The positive effect of plant diversity on soil carbon depends on climate

Little is currently known about how climate modulates the relationship between plant diversity and soil organic carbon and the mechanisms involved. Yet, this knowledge is of crucial importance in times of climate change and biodiversity loss. Here, we show that plant diversity is positively correlated with soil carbon content and soil carbon-to-nitrogen ratio across 84 grasslands on six continents that span wide climate gradients. The relationships between plant diversity and soil carbon as well as plant diversity and soil organic matter quality (carbon-to-nitrogen ratio) are particularly strong in warm and arid climates. While plant biomass is positively correlated with soil carbon, plant biomass is not significantly correlated with plant diversity. Our results indicate that plant diversity influences soil carbon storage not via the quantity of organic matter (plant biomass) inputs to soil, but through the quality of organic matter. The study implies that ecosystem management that restores plant diversity likely enhances soil carbon sequestration, particularly in warm and arid climates

Phosphorus and carbon in soil particle size fractions : A synthesis

Despite the importance of phosphorus (P) as a macronutrient, the factors controlling the pool sizes of organic and inorganic P (OP and IP) in soils are not yet well understood. Therefore, the aim of this study was to gain insights into the pools sizes of OP, IP and organic carbon (OC) in soils and soil particle size fractions. For this purpose, I analyzed the distribution of OP, IP, and OC among particle size fractions depending on geographical location, climate, soil depth, and land use, based on published data. The clay size fraction contained on average 8.8 times more OP than the sand size fraction and 3.9 and 3.2 times more IP and OC, respectively. The OP concentrations of the silt and clay size fraction were both negatively correlated with mean annual temperature (R2 = 0.30 and 0.31, respectively, p < 0.001). The OC:OP ratios of the silt and clay size fraction were negatively correlated with latitude (R2 = 0.49 and 0.34, respectively, p < 0.001). Yet, the OC:OP ratio of the clay size fraction changed less markedly with latitude than the OC:OP ratio of the silt and the sand size fraction. The OC concentrations of all three particle size fractions were significantly (p < 0.05) lower in soils converted to cropland than in adjacent soils under natural vegetation. In contrast, the OP concentration was only significantly (p < 0.05) decreased in the sand size fraction but not in the other two particle size fractions due to land-use change. Thus, the findings suggest that OP is more persistent in soil than OC, which is most likely due to strong sorptive stabilization of OP compounds to mineral surfaces

Mechanismen der Phosphor-Akquise von Nutzpflanzen in Mischkulturen: Die Rolle von Phosphatasen und pH-Änderungen in der Rhizosphäre

Forschungsarbeiten der letzten Jahre zeigten, dass Mischkulturen zu einer gesteigerten Phosphor (P)-Aufnahme von Nutzpflanzen und folglich zu gesteigerten Erträgen beitragen können. Die zugrundeliegenden Mechanismen der P-Akquise sind allerdings noch kaum bekannt. Ziel der Studie war es deshalb, die potentiellen Mechanismen in einem Mischkultur-Experiment zu untersuchen. Wir analysierten die pH-Änderungen und Phosphatase-Aktivitäten in der Rhizosphäre von Mais (Zea mays) in Mischkultur mit entweder Ackerbohne (Vicia faba), Blauer Süßlupine (Lupinus angustifolius) oder Weißem Senf (Sinapis alba) im Vergleich mit Mais in Monokultur. Dafür wurden die Pflanzen in Rhizoboxen kultiviert; die Phosphatase-Aktivität wurde mittels Boden-Zymographie und die pH-Änderung mithilfe von pH-Indikator-Gelen untersucht. Zusätzlich wurde mit den gleichen Pflanzen ein Feldversuch durchgeführt, um die Effekte der Nebenkulturen auf die Mais-Biomasseproduktion zu untersuchen. Erste Ergebnisse legen nahe, dass die gewählten Pflanzen unterschiedliche Mechanismen der P-Akquise nutzen (Rhizoboxen-Experiment), die mit unterschiedlichen Maiserträgen einhergehen (Feldversuch)

Carbon, nitrogen, and phosphorus stoichiometry of organic matter in Swedish forest soils and its relationship with climate, tree species, and soil texture

While the carbon (C) content of temperate and boreal forest soils is relatively well studied, much less is known about the ratios of C, nitrogen (N), and phosphorus (P) of the soil organic matter, as well as the abiotic and biotic factors that shape them. Therefore, the aim of this study was to explore carbon, nitrogen, and organic phosphorus (OP) contents and element ratios in temperate and boreal forest soils and their relationships with climate, dominant tree species, and soil texture. For this purpose, we studied 309 forest soils located all over Sweden between 56 and 68 degrees N. The soils are a representative subsample of Swedish forest soils with a stand age > 60 years that were sampled for the Swedish Forest Soil Inventory. We found that the N stock of the organic layer increased by a factor of 7.5 from -2.0 to 7.5 degrees C mean annual temperature (MAT), which is almost twice as much as the increase in the organic layer stock along the MAT gradient. The increase in the N stock went along with an increase in the N : P ratio of the organic layer by a factor of 2.1 from -2.0 to 7.5 degrees C MAT (R-2 = 0.36, p < 0.001). Forests dominated by pine had higher C : N ratios in the organic layer and mineral soil down to a depth of 65 cm than forests dominated by spruce. Further, also the C : P ratio was increased in the pine-dominated forests compared to forests dominated by other tree species in the organic layer, while the C : OP ratio in the mineral soil was not elevated in pine forests. C, N, and OP contents in the mineral soil were higher in fine-textured soils than in coarse-textured soils by a factor of 2.3, 3.5, and 4.6, respectively. Thus, the effect of texture was stronger on OP than on N and C likely because OP adsorbs very rigidly to mineral surfaces. Further, we found that the P and K concentrations of the organic layer were inversely related to the organic layer stock, while the N : P ratio was positively related to the organic layer stock. Taken together, the results show that the N : P ratio of the organic layer was most strongly related to MAT. Further, the C : N ratio was most strongly related to dominant tree species even in the mineral subsoil. In contrast, the C : P ratio was only affected by dominant tree species in the organic layer, but the C : OP ratio in the mineral soil was hardly affected by tree species due to the strong effect of soil texture on the OP concentration

Plant Species Interactions in the Rhizosphere Increase Maize N and P Acquisition and Maize Yields in Intercropping

The aim of the study was to examine interspecific plant interactions that contribute to plant nitrogen (N) and phosphorus (P) acquisition and are likely the reason for overyielding in intercropping. We conducted a field and a rhizobox experiment with the same soil. Maize (Zea mays L.) was grown alone or intercropped with the companions faba bean (Vicia faba L.), soy (Glycine max (L.) Merr.), blue lupin (Lupinus angustifolius L.), or white mustard (Sinapis alba L.). We determined the isotopic N signature (delta N-15) of maize as well as soil parameters (pH, phosphatase activity, nitrate) in the field experiment. We analyzed phosphatase activities and rhizosphere pH by soil zymography and pH imaging in the rhizobox experiment. Maize N and P contents were larger in intercropping than monocropping, especially with soy and lupin in the field, indicating intercropping advantages for maize N and P acquisition. Intercropping with legumes decreased maize delta N-15 in the field, suggesting that 11-20% of maize aboveground biomass N was transferred from legumes to maize. Soil zymography revealed high phosphatase activities in the rhizosphere of lupin and faba bean. pH imaging showed a rhizosphere alkalinization by mustard, and a rhizosphere acidification by faba bean. These changes in the companions' rhizosphere likely mobilized P and were also beneficial for maize in intercropping. Taken together, our study provides evidence that the companions' ability to mobilize N and P in the rhizosphere promotes increases in maize nutrient contents and causes maize overyielding in intercropping and thus can contribute to fertilizer savings

Spatial patterns of nitrogen isotope ratios in forest soils are related to latitude and soil phosphorus concentration

The aim of this study was to identify the parameters that affect the nitrogen (N) isotope ratio (& delta;N-15) in soils of temperate and boreal forests. We measured the & delta;N-15 in 30 soil profiles of temperate and boreal forests in Sweden and analyzed the relationships between & delta;N-15 in the soils and soil chemical properties as well as site characteristics. In addition, we conducted a meta-analyses of & delta;N-15 in the organic layer of European forests. We identified two types of & delta;N-15 patterns; in type D soils, the & delta;N-15 in the mineral soil decreases with depth, whereas in type C soil, the & delta;N-15 in the soil profile is almost constant. Type D soils had a significantly higher & delta;N-15 in the organic layer and upper mineral soil than type C soils, which is likely due to N isotope fractionation by ectomycorrhizal fungi in the topsoil. Type D soils were found in boreal forests, but not in temperate forests. They had a significantly lower atmospheric N deposition rate than type C soils, by a factor of 2.3, and a significantly higher phosphorus (P) concentration of the organic layer than type C soils, by a factor of 1.5. We also found that the & delta;N-15 was negatively correlated with the N:P ratio of the organic layer (R-2 = 0.21, p < 0.001). Across Europe, the & delta;N-15 of the organic layer was positively correlated with latitude (R-2 = 0.58, p < 0.001), and negatively with mean annual temperature (R-2 = 0.52, p < 0.001) and atmospheric N deposition (R-2 = 0.42, p < 0.001). In conclusion, our results show that the & delta;N-15 of the organic layer and microbial N (re-)cycling in forest soils is positively related with latitude and the P concentration of the organic layer

Soil carbon and nitrogen contents in forest soils are related to soil texture in interaction with pH and metal cations

The aim of this study was to better understand how soil carbon (C) and nitrogen (N) contents and the C:N ratio are related to soil texture, pH, and exchangeable aluminum and calcium in forest soils.For this purpose, we studied 1992 temperate and boreal forest soils located all over Sweden. We measured organic C and N as well exchangeable aluminum, calcium, and pH in the organic layer and three depth increments in the mineral soil (down to 65 cm), and analyzed the relationship between element contents, soil texture, and soil pH as well as their interactions.Soil C concentration and the C:N ratio were negatively related to soil pH. The C concentration was on average 2.6 times higher in very acidic soils (pH 5.0, in the uppermost 10 cm of the mineral soil. In contrast, N varied much less with pH, particularly in the organic layer, but was related to soil texture. The N concentration was 2.3 times higher in clayey and fine silty soils than in sandy soils, while the C concentration was only 1.85 times higher in clayey and fine silty soils than in sandy soils (in the uppermost 10 cm). Differences in C and N concentrations between clayey and fine silty soils compared to sandy soils were largest in the class of soils with pH > 5.0 and smallest in the class of soils with pH <= 4.0. Furthermore, C and N concentrations were both positively correlated with the concentration of exchangeable aluminum in the mineral soil, and these correlations were stronger in coarse-textured than in fine-textured soils. In addition, the C concentration was positively correlated with the concentration of exchangeable calcium in the organic layer.In conclusion, our results show that C concentration varied much more strongly with pH than N concentration, likely due to effects of pH on microbial respiration. The N concentration was more strongly related to soil texture than the C concentration, which is very likely due to the high charge density of organic N, which gives organic N a high affinity to adsorb to mineral surfaces. Furthermore, exchangeable aluminum seems to play an important role in the sorptive stabilization of organic matter in the mineral soil