Andreas P. Mamolos

Depth of Root Activity of Coexisting Grassland Species in Relation to N and P Additions, Measured Using Nonradioactive Tracers

1 Root activity of coexisting plant species was assessed by injecting lithium, strontium and caesium at depths of 5 and 15 cm in the soil of an upland grassland to which a factorial combination of N and P additions had been applied. 2 For.each species and each tracer the ratio of the above-ground concentrations after injection at depths of 5 and 15 cm was calculated and the species ranked for each tracer in order of root activity with soil depth; Sr and Cs gave similar results, which in some cases were quite different from those with Li. 3 When Cs and Sr were injected at the depth of 5 cm, a positive correlation was evident between Sr and Ca concentrations for the various species but not for Cs and K. 4 Although root activity was higher at a depth of 5cm for all species, the relative activity with depth differed between species; Agrostis capillaris, the most abundant species, and Thymus sibthorpii had deeper root activity than Carex caryophyllea, the second most abundant species, and Teucrium chamaedrys. 5 When N and/or P were added Agrostis capillaris and Carex caryophyllea tended to become shallower rooted and their above-ground biomass increased; for these species a positive correlation was evident between relative abundance and ratios of concentrations, indicating that the most competitive species tended to become shallower rooted when the limiting nutrients were added. 6 Ranking of species in root activity with depth differed among the various nutrient treatments. Legumes tended to have the deepest root activity when N only was applied and the shallowest root activity when P was applied. 7 Although the ranking of species was influenced by the availability of nutrients, the hypothesis that the less competitive species are forced to deeper rooting was not clearly supported; the legume species Trifolium heldreichianum only tended to become deeper rooted when N was added, i.e. in the treatment in which it was less competitive.

Decomposition of dominant plant species litter in a semi-arid grassland

Abstract Dominant plant species in semi-arid environments differ in their effects on litter decomposition. The present study was conducted to investigate the contribution of dominant plant species found in a natural semi-arid grassland to nutrient cycling through their litter decomposition. Aboveground litter (stems and leaves) of Dichanthium ischaemum , Chrysopogon gryllus , Festuca ovina and Trifolium purpureum was placed on the soil for 24 months and chemical characteristics were monitored. The rate of mass loss from stems was significantly lower than that of leaves for all species. The influence of mesh size on the studied parameters for both leaves and stems was similar in most cases for the grass species, Chrysopogon and Festuca (e.g. litter, lignin, TNSC, Energy and Total C, N, K, Ca). Generally, mean decomposition rate ( k ′= k ×10 5 ) had the highest value for Trifolium ( k ′=188), followed by Dichanthium ( k ′=133), Chrysopogon ( k ′=120) and Festuca ( k ′=118). Chrysopogon and Festuca by being the most dominant species in the grassland and having low decomposition rates contribute more organic matter to the soil.

Plant Species Abundance and Tissue Concentrations of Limiting Nutrients in Low-Nutrient Grasslands: A Test of Competition Theory

1 A 3-year study tested the hypothesis that proportions of plant species are negatively related to species concentrations of limiting nutrients using a moderately acid lowland grassland site in Northern Greece, where growth was limited by soil moisture, N and P. 2 Species proportions were assessed both by a cumulative measure (above-ground biomass duration for the whole growth period) and by yield at the peak of aboveground biomass of the community. Weighted N, P and K concentrations of species for the whole growth period were calculated by dividing above-ground N or P or K content duration by above-ground biomass duration. 3 Measurements during one growth period (seven samplings from mid March to mid June in 1991) showed that biomass was higher in roots than in shoots for most species examined. For total grasses and Rumex acetosella total N and P were higher in roots than in the shoot for the whole growth period. The dicot species Cichorium intybus, Hypochoeris radicata and Plantago lanceolata contained more N and P in shoots than in roots after mid April. 4 Weighted N, P and K concentrations of shoots were positively related to their respective concentrations of whole plants. 5 Addition of either N or P increased community productivity and changed species composition, especially in years when soil moisture was adequate. 6 Proportions of species were negatively related to weighted N concentrations of species. 7 Species with higher than average N or P concentrations showed the greatest relative increases when soil was enriched with N or P, respectively. 8 These results seem to be consistent with the regulation of species abundance by competition-driven nutrient depletion.

Litter dynamics of low and high tannin sericea lespedeza plants under field conditions

Sericea lespedeza [Lespedeza cuneata (Dum. Cours) G. Don.] is a perennial legume with high polyphenol (tannin) concentration. The decomposition and nutrient release of sericea lespedeza residues with two tannin levels (high = 22% or low = 16%), which were either placed on the soil surface or buried at a depth of 5 cm were studied. An experiment was carried out at two sites for 2 yr. Litter mass loss and nutrient (N, P, K, Ca, Mg, Cu, Fe, Mn, Zn, B, Mo, Co) release were recorded. Litter mass loss was higher for the low-tannin residues and for those buried. From the beginning of the experiments, the C : N ratio was lower than 25 : 1 and N was mineralized for most of the studied cases; this means that N increased in availability to plants. The release of the rest of the studied nutrients was higher at the depth of 5 cm than on the soil surface and higher for low-tannin residues than for high-tannin. The observed accumulation of some nutrients in the first months presumably depended on microbial activity. The rate of release was higher for the macronutrients than for the micronutrients, with the exception of B, which had the same behaviour as the macronutrients.

Vegetation in contrasting soil water sites of upland herbaceous grasslands and N:P ratios as indicators of nutrient limitation

Effects of differences in long-term water supply were examined on soil characteristics, primary production and species composition in a wet and a dry site of an upland herbaceous grassland. Also the responses of species to N and P enrichments were examined. N and P concentrations of non-legume species were positively related, indicating that biomass N:P ratios seem to be mainly determined by N:P supply ratios. Forbs had generally higher concentrations than graminoids. Intermittent water inundation of soil in the wet site resulted in greater soil N and P availability. The greater productivity of this site promoted the growth of forbs. A fertilizer experiment showed that biomass was limited by N only in the wet site, but by both nutrients in the dry one. The species with the higher N and P concentrations were favored more after N and P enrichment, respectively; however, species enhancement was not related to N:P ratios of species. This indicates that N and P concentrations of species, rather than N:P ratios of species, are better predictors of species responses to N and P enrichment. N:P ratios of whole communities were 8.73 for the wet and 11.36 for the dry site. These values in comparison with the responses of plant communities to N and P fertilization show that thresholds of N:P ratios indicative of N or P limitation are much lower than those found for European wetlands.

Medium-term fertilization of grassland plant communities masks plant species-linked effects on soil microbial community structure

According to the singular hypothesis of plant diversity, different plant species are expected to make unique contributions to ecosystem functioning. Hence, individual species would support distinct microbial communities. It was hypothesized that microbial community dynamics in the respective rhizospheres of, two floristically divergent species, Agrostis capillaris and Prunella vulgaris that were dominant in a temperate, upland grassland in northern Greece, would support distinct microbial communities, in agreement to the singular hypothesis. Phospholipid lipid fatty acid (PLFA) profiles of the rhizosphere soil microbial community were obtained from the grassland which had been subjected to factorial nitrogen (N) and phosphorus (P) fertilization over five plant growth seasons. The soil cores analyzed were centered on stands of the two co-occurring target plant species, sampled from five blocks in all four factorial N and P fertilization combinations. Distinct PLFA clustering patterns following principle component analysis of PLFA concentrations revealed that, in the absence of P fertilization, soils under the two plant species supported divergent microbial communities. In the P fertilized plots, however, no such distinction could be observed. Results reveal that nutrient fertilization may mask the ability of plant species to shape their own rhizosphere microbial community.

Nutrient release from decomposing Lotus corniculatus residues in relation to soil pH and nitrogen levels

The rate of biomass decomposition, organic matter loss, and nutrient release from litter of Lotus corniculatus grown with or without N were studied using the litter-bag technique. The experiments were carried out at two sites in northern Greece with soil pH of 7.8 and 5.6, respectively. Applied N increased biomass decomposition and total N release in the neutral soil and decreased organic matter loss and total N release in the acid soil. Nitrogen application increased P, Na and Mg release in the neutral soil and decreased Ca release in the acid soil. Without N application nutrient release was greater in the acid than in the neutral soil. Soil acidity appeared to have important consequences for how elements cycle through litter and soil, probably because of reduced faunal and microbial decomposition and increased levels of organic matter.

Competition between Canada thistle and winter wheat

Abstract This study was conducted to determine the effect of Canada thistle density and the direct and indirect effects of Canada thistle aboveground biomass and N concentration on wheat yield. A 4-yr experiment (1991–1995) with four Canada thistle densities (0, 4, 16, 64 plants m−2) was conducted. Initial statistical analysis showed a significant effect of Canada thistle density on wheat yield. Multiple regression and path analysis showed that the main factor causing wheat yield loss was Canada thistle N concentration. The second factor affecting wheat yield was Canada thistle biomass, and the last was Canada thistle density. Nomenclature: Canada thistle, Cirsium arvense (L.) Scop. CIRAR; winter wheat, Triticum aestivum (L.) Em. Tell. ‘Yecora’.

Differentiation between responses of primary productivity and phosphorus exploitation to species richness

Several studies have shown that ecosystem functioning increases with increasing species richness. Most of these studies examined the effects of species richness on primary productivity. The underlying mechanism that explains this pattern is usually the selection effect. The higher the diversity in plant communities the higher the chance in including a very productive species that dominates the community, or a legume species that brings N into the soil. Less attention has been given so far to the effects of species richness on phosphorus exploitation. The aim of this work was to investigate the effect of species richness on aboveground primary productivity and P accumulation in a plant diversity experiment. For this reason, 14 grassland plant species were grown in containers as monocultures and in mixtures of 2-, 3-, 4-, 8-, 11- and 14-species combinations. Results show that the aboveground phytomass and total P increased with increasing species richness. Complementarity effects, probably through partitioning of resources, were most apparent in the highest levels of species richness, and were observed to be greater for total P in comparison to phytomass. Selection effects generally were greater for phytomass than for total P; they were significantly positive at the 2- to 8-species combinations but close to 0 or negative in the highest levels of species richness. The increases in phytomass and total P at the highest levels of species richness appeared to be caused by the increased performance of intermediate-productive species.

Spatial variation in a grassland on soil rich in heavy metals

The vegetation in a grassland area in the prefecture of Kilkis (N. Greece), known for its surface Cu-mineralization, was studied. 43 quadrats were established along a transect through an area where the vegetation formed patches of differ- ent size. Cover-abundance and frequency estimates for all species were made. Normal Association Analysis revealed five quadrat groups characterized by Trifolium scabrum, Linaria pelisseriana, Anthoxanthum ovatum, Gypsophila muralis and Minuartia hirsuta ssp. falcata. 43 soil samples were analysed for pH, organic C, CaCO3, total content of Fe, Zn, Pb, Cu, Mn, Ca, Mg, K, Na and soil texture. From a discriminant analysis performed on soil data five soil groups resulted, which are highly related to the five vegetation groups. Thymus sihthorpii, Minuartia hirsuta ssp. falcata and Rumex acetosella are the most important taxa with respect to physiognomy and patchi- ness of the vegetation. The number of species in each group of quadrats is affected by the relative favourableness or severity of the soil conditions. Metal contents, mainly Zn, Cu, Mg and Na, and soil texture are considered to be among the main factors controlling the structure and physiognomy of the veg- etation.