Large‐scale pattern of biomass partitioning across China's grasslands

Aim To investigate large‐scale patterns of above‐ground and below‐ground biomass partitioning in grassland ecosystems and to test the isometric theory at the community level. Location Northern China, in diverse grassland types spanning temperate grasslands in arid and semi‐arid regions to alpine grasslands on the Tibetan Plateau. Methods We investigated above‐ground and below‐ground biomass in China's grasslands by conducting five consecutive sampling campaigns across the northern part of the country during 2001–05. We then documented the root : shoot ratio (R/S) and its relationship with climatic factors for China's grasslands. We further explored relationships between above‐ground and below‐ground biomass across different grassland types. Results Our results indicated that the overall R/S of China's grasslands was larger than the global average (6.3 vs. 3.7). The R/S for China's grasslands did not show any significant trend with either mean annual temperature or mean annual precipitation. Above‐ground biomass was nearly proportional to below‐ground biomass with a scaling exponent (the slope of log–log linear relationship between above‐ground and below‐ground biomass) of 1.02 across various grassland types. The slope did not differ significantly between temperate and alpine grasslands or between steppe and meadow. Main conclusions Our findings support the isometric theory of above‐ground and below‐ground biomass partitioning, and suggest that above‐ground biomass scales isometrically with below‐ground biomass at the community level.     

Above‐ and belowground biomass allocation in Tibetan grasslands

Question: Optimal partitioning and isometric allocation are two important hypotheses in plant biomass allocation. We tested these two hypotheses at the community level, using field observations from Tibetan grasslands. Location: Qinghai‐Tibetan Plateau, China. Methods: We investigated allocation between above‐ and belowground biomass in alpine grasslands and its relationship with environmental factors using data collected from 141 sites across the plateau during 2001‐2005. We used reduced major axis (RMA) regression and general linear models (GLM) to perform data analysis. Results: The median values of aboveground biomass (M_A), belowground biomass (M_B), and root:shoot (R:S) ratio in alpine grasslands were 59.7, 330.5 g m^?2, and 5.8, respectively. About 90% of total root biomass occurred in the top 30 cm of soil, with a larger proportion in the alpine meadow than in the alpine steppe (96 versus 86%). As soil nitrogen and soil moisture increased, both M_A and M_B increased, but R:S ratio did not show a significant change. M_A scaled as 0.92 the power of M_B, with 95% confidence intervals of 0.82‐1.02. The slope of the isometric relationship between log M_A and log M_B did not differ significantly between alpine steppe and alpine meadow. The isometric relationship was also independent of soil nitrogen and soil moisture. Conclusions: Our results support the isometric allocation hypothesis for the M_A versus M_B relationship in Tibetan grasslands.     

Above- and belowground biomass allocation and its regulation by plant density in six common grassland species in China

Above- and belowground biomass allocation is an essential plant functional trait that reflects plant survival strategies and affects belowground carbon pool estimation in grasslands. However, due to the difficulty of distinguishing living and dead roots, estimation of biomass allocation from field-based studies currently show large uncertainties. In addition, the dependence of biomass allocation on plant species, functional type as well as plant density remains poorly addressed. Here, we conducted greenhouse manipulation experiments to study above- and belowground biomass allocation and its density regulation for six common grassland species with different functional types (i.e., C₃ vs C₄; annuals vs perennials) from temperate China. To explore the density regulation on the biomass allocation, we used five density levels: 25, 100, 225, 400, and 625 plant m^?2. We found that mean root to shoot ratio (R/S) values ranged from 0.04 to 0.92 across the six species, much lower than those obtained in previous field studies. We also found much lower R/S values in annuals than in perennials (C. glaucum and S. viridis vs C. squarrosa, L. chinensis, M. sativa and S. grandis) and in C₄ plants than in C₃ plants (C. squarrosa vs L. chinensis, M. sativa and S. grandis). In addition to S. grandis, plant density had significant effects on the shoot and root biomass fraction and R/S for the other five species. Plant density also affected the allometric relationships between above- and belowground biomass significantly. Our results suggest that R/S values obtained from field investigations may be severely overestimated and that R/S values vary largely across species with different functional types. Our findings provide novel insights into approximating the difficult-to-measure belowground living biomass in grasslands, and highlight that species composition and intraspecific competition will regulate belowground carbon estimation.

     

Leaf meristems: an easily ignored component of the response to human disturbance in alpine grasslands

Grazing and fencing are two important factors that influence productivity and biomass allocation in alpine grasslands. The relationship between root (R) and shoot (S) biomass and the root:shoot ratio (R/S) are critical parameters for estimating the terrestrial carbon stocks and biomass allocation mechanism responses to human activities. Previous studies have often used the belowground:aboveground biomass ratio (M_b/M_a) to replace the R/S in alpine ecosystems. However, these studies may have neglected the leaf meristem biomass, which belongs to the shoot but occurs below the soil surface, leading to a significant overestimation of the R/S ratio. We conducted a comparative study to explore the differences between the R/S and M_b/M_a at both the species (Stipa purpurea, Carex moorcroftii, and Artemisia nanschanica) and community levels on a Tibetan alpine grassland with grazing and fencing management blocks. The results revealed that the use of the M_b/M_a to express the R/S appeared to overestimate the actual value of the R/S, both at species and community levels. For S. purpurea, the M_b/M_a was three times higher than the R/S. The M_b/M_a was approximately two times higher than the R/S for the species of C. moorcroftii and A. nanschanica and at the community level. The relationships between the R‐S and M_b‐M_a exhibited different slopes for the alpine plants across all the management practices. Compared to the fenced grasslands, the plants in the grazing blocks not only allocated more biomass to the roots but also to the leaf meristems. The present study highlights the contribution of leaf meristems to the accurate assessment of shoot and belowground biomasses. The R/S and M_b/M_a should be cautiously used in combination in the future research. The understanding of the distinction between the R‐S and M_b‐M_a may help to improve the biomass allocation mechanism response to human disturbances in an alpine area.     

Estimating root biomass in Salix viminalis × Salix schwerinii cultivar “Olof” using the electrical capacitance method

Abstract

Non‐destructive assessment of root systems is important in order to understand and optimise the potential of resource capture and allocation by the plant. We studied the relationships between electrical capacitance (EC) and the below‐ and above‐ground biomass of willows. Cuttings of Salix viminalis × Salix schwerinii cv. Olof were maintained in pots and root development was followed up using a portable capacitance meter over the course of 2.5 months. Pot observations were compared with excavation of two‐year‐old established trees. A strong significant linear relationship (R ² = 0.81, p < 0.001) was obtained between EC and root biomass (dry weight [DW]) for the pot experiment. EC also showed good correlations with stem and leaf biomass, as well as with stem height. In the excavated willow trees, there was a strong logarithmic relationship between EC and root biomass (R ² = 0.66, p < 0.001). These results suggest that EC is a good estimator of below‐ground biomass in willow and may become useful in screening varieties for differences in root biomass traits, especially in distinguishing below‐ground resource allocation at an early stage.     

青藏高原高寒灌丛生态系统草本层生物量分配格局

青藏高原高寒灌丛生态系统生物量分配的研究相对较少,尤其是其草本层。为了探究高寒灌丛生态系统草本层生物量分配特征及其影响因素,分析了青藏高原东北部灌丛生态系统的49个高寒灌丛样地的草本层地上与地下生物量特征及其气候因子之间的关系。结果表明1)草本层地上生物量与地下生物量分别为121.1,342.8 g/m2均大于高寒草地的地上生物量与地下生物量。2)草本层的根冠比为3.6低于高寒草地的根冠比。3)地上生物量与地下生物量之间呈现幂函数的关系y=8.0x0.83(R2=0.48,P0.001)。4)根冠比与年均温度、年均降雨量之间没有显著的相关关系。     

A regional‐scale consideration of the effects of species richness on above‐ground biomass in temperate natural grasslands of China

Question: Can species richness be a predictor for above‐ground biomass in natural grasslands at a regional scale? Location: A total of 647 sites across temperate natural grasslands of northern China. Methods: Structural equation modelling (SEM) was used to examine the effect of species richness on above‐ground biomass. Asymptotically distribution‐free estimation was selected for parameter estimation. The SEM process was performed at five sample sizes (n=50, 100, 200, 300 and 647). Spatial structure in the original data was examined by calculating Moran's I. Results: SEM run at n=647 revealed a positive effect of species richness on above‐ground biomass after controlling for the influences of bioclimatic factors and grazing. At the four reduced sample size levels, the positive effect held true for most cases in 400 observations (>92%). Conclusions: Contrary to observations in previous studies in natural grasslands, our data showed a positive effect of species richness on above‐ground biomass. This suggests that, as a short‐term effect of diversity on productivity, niche complementarity among coexisting species tends to be an important process in arid and semi‐arid natural grasslands. We hold that biodiversity conservation is among the fundamental approaches required to maintain productivity of grasslands in arid and semi‐arid areas.     

Grass allometry and estimation of above‐ground biomass in tropical alpine tussock grasslands

The puna/páramo grasslands span across the highest altitudes of the tropical Andes, and their ecosystem dynamics are still poorly understood. In this study we examined the above‐ground biomass and developed species specific and multispecies power‐law allometric equations for four tussock grass species in Peruvian high altitude grasslands, considering maximum height (h_max), elliptical crown area and elliptical basal area. Although these predictors are commonly used among allometric literature, they have not previously been used for estimating puna grassland biomass. Total above‐ground biomass was estimated to be of 6.7 ± 0.2 Mg ha^?1 (3.35 ± 0.1 Mg C ha^?1). All allometric relationships fitted to similar power‐law models, with basal area and crown area as the most influential predictors, although the fit improved when tussock maximum height was included in the model. Multispecies allometries gave better fits than the other species‐specific equations, but the best equation should be used depending on the species composition of the target grassland. These allometric equations provide an useful approach for measuring above‐ground biomass and productivity in high‐altitude Andean grasslands, where destructive sampling can be challenging and difficult because of the remoteness of the area. These equations can be also applicable for establishing above‐ground reference levels before the adoption of carbon compensation mechanisms or grassland management policies, as well as for measuring the impact of land use changes in Andean ecosystems.     

Seeds of change: The value of using Rhinanthus minor in grassland restoration

Question: What is the value of using Rhinanthus minor in grassland restoration and can restrictions on its establishment be overcome? Location: England (United Kingdom). Methods: Two experiments were established to determine the efficacy of inoculating R. minor on a suite of four agriculturally improved grasslands and the efficacy of using R. minor in grassland restoration. In Experiment 1, the effect of herbicide gap creation on the establishment and persistence of R. minor in grasslands ranging in productivity was investigated with respect to sward management. In Exp. 2, R. minor was sown at 1000 seeds/m² in conjunction with a standard meadow mix over a randomized plot design into Lolium perenne grassland of moderate productivity. The treatment of scarification was investigated as a treatment to promote R. minor. Results: Gap size had a significant role in the establishment and performance of R. minor, especially the 30 cm diameter gaps (Exp. 1). However, R. minor failed to establish long‐term persistent populations in all of the agriculturally improved grasslands. In Exp. 2, establishment of R. minor was increased by scarification and its presence was associated with a significant increase in Shannon diversity and the number of sown and unsown species. Values of grass above‐ground biomass were significantly lower in plots sown with R. minor, but values of total above‐ground biomass (including R. minor) and forb biomass (not including R. minor) were not affected. Conclusions: The value of introducing R. minor into species‐poor grassland to increase diversity has been demonstrated, but successful establishment was dependent on grassland type. The scope for using R. minor in grassland restoration schemes is therefore conditional, although establishment can be enhanced through disturbance such as sward scarification.     

Patterns of above- and belowground biomass allocation in China’s grasslands: Evidence from individual-level observations

Above- and belowground biomass allocation not only influences growth of individual plants, but also influences vegetation structures and functions, and consequently impacts soil carbon input as well as terrestrial ecosystem carbon cycling. However, due to sampling difficulties, a considerable amount of uncertainty remains about the root: shoot ratio (R/S), a key parameter for models of terrestrial ecosystem carbon cycling. We investigated biomass allocation patterns across a broad spatial scale. We collected data on individual plant biomass and systematically sampled along a transect across the temperate grasslands in Inner Mongolia as well as in the alpine grasslands on the Tibetan Plateau. Our results indicated that the median of R/S for herbaceous species was 0.78 in China’s grasslands as a whole. R/S was significantly higher in temperate grasslands than in alpine grasslands (0.84 vs. 0.65). The slope of the allometric relationship between above- and belowground biomass was steeper for temperate grasslands than for alpine. Our results did not support the hypothesis that aboveground biomass scales isometrically with belowground biomass. The R/S in China’s grasslands was not significantly correlated with mean annual temperature (MAT) or mean annual precipitation (MAP). Moreover, comparisons of our results with previous findings indicated a large difference between R/S data from individual plants and communities. This might be mainly caused by the underestimation of R/S at the individual level as a result of an inevitable loss of fine roots and the overestimation of R/S in community-level surveys due to grazing and difficulties in identifying dead roots. Our findings suggest that root biomass in grasslands tended to have been overestimated in previous reports of R/S.     

施肥对香樟幼苗生长及养分分配的影响

施肥是苗木培育的重要方式,香樟是乡土珍稀阔叶树种,苗木培育对乡土珍稀树种的保护、繁育、推广具有极其重要的作用,施肥对苗木的生长和发育具有重要的影响。因此,为了探讨香樟幼苗生长及植物体内养分分配对施肥的响应,该研究采用正交设计,设置了氮、磷、钾3因素3水平(N、P:0、3、6 g·株-1;K:0、2、4g·株-1),对盆栽香樟幼苗进行指数施肥。结果表明:(1)氮肥对香樟幼苗苗高、地径、生物量的影响最为显著,磷肥和钾肥的影响则较小;(2)氮素在香樟幼苗叶、茎、根中的分布状况主要受氮肥的影响,磷素在香樟幼苗叶、茎、根中的分布状况主要受氮肥和磷肥的影响,钾素在香樟幼苗叶、茎、根中的分布状况主要受钾肥的影响;(3)香樟幼苗的苗高生长与叶片氮含量、叶片磷含量呈显著正相关(P0.05),地径生长与茎氮含量呈显著正相关(P0.05),叶生物量与叶片氮含量、叶片磷含量呈显著正相关(P0.05),茎生物量与叶片磷含量呈显著正相关(P0.05);(4)综合分析得出,对香樟幼苗苗高、地径生长,以及枝叶生物量积累最具促进作用的施肥水平为氮肥(6 g·株-1)、磷肥(6 g·株-1)、钾肥(4 g·株-1)。     

Above‐ and below‐ground plant biomass response to experimental warming in northern Alaska

Question: Does experimental warming, designed to simulate future warming of the Arctic, change the biomass allocation and mycorrhizal infection of tundra plants? Location: High Arctic tundra near Barrow, Alaska, USA (71°18′N 156°40′W). Methods: Above and below ground plant biomass of all species was harvested following 3–4 yr of 1‐2°C of experimental warming. Biomass allocation and arbuscular mycorrhizal infection were also examined in the two dominant species, Salix rotundifolia and Carex aquatilis. Results: Above‐ground biomass of graminoids increased in response to warming but there was no difference in total plant biomass or the ratio of above‐ground to below‐ground biomass for the community as a whole. Carex aquatilis increased above‐ground biomass and proportionally allocated more biomass above ground in response to warming. Salix rotundifolia increased the amount of above‐ and below‐ground biomass allocated per leaf in response to warming. Mycorrhizal infection rates showed no direct response to warming, but total abundance was estimated to have likely increased in response to warming owing to increased root biomass of S. rotundifolia. Conclusions: The community as a whole was resistant to short‐term warming and showed no significant changes in above‐ or below‐ground biomass despite significant increases in above‐ground biomass of graminoids. However, the patterns of biomass allocation for C. aquatilis and S. rotundifolia did change with warming. This suggests that long‐term warming may result in changes in the above‐ground to below‐ground biomass ratio of the community.     

Differential effect of drought regimes on the seedling performance of six floodplain grassland species

• The performance of seedlings is crucial for the survival and persistence of plant populations. Although drought frequently occurs in floodplains and can cause seedling mortality, studies on the effects of drought on seedlings of floodplain grasslands are scarce. We tested the hypotheses that drought reduces aboveground biomass, total biomass, plant height, number of leaves, leaf area and specific leaf area (SLA), and increases root biomass and root‐mass fraction (RMF) and that seedlings from species of wet floodplain grasslands are more affected by drought than species of dry grasslands.
• In a greenhouse study, we exposed seedlings of three confamilial pairs of species (Pimpinella saxifraga, Selinum carvifolia, Veronica teucrium, Veronica maritima, Sanguisorba minor, Sanguisorba officinalis) to increasing drought treatments. Within each plant family, one species is characteristic of wet and one of dry floodplain grasslands, confamilial in order to avoid phylogenetic bias of the results.
• In accordance with our hypotheses, drought conditions reduced aboveground biomass, total biomass, plant height, number of leaves and leaf area. Contrary to our hypotheses, drought conditions increased SLA and decreased root biomass and RMF of seedlings. Beyond the effects of the families, the results were species‐specific (V. maritima being the most sensitive species) and habitat‐specific. Species indicative of wet floodplain grasslands appear to be more sensitive to drought than species indicative of dry grasslands.
• Because of species‐ and habitat‐specific responses to reduced water availability, future drought periods due to climate change may severely affect some species from dry and wet habitats, while others may be unaffected.

     

Effect of Seed Treatment with Rhizobium leguminosarum on Pythium Damping-off, Seedling Height, Root Nodulation, Root Biomass, Shoot Biomass, and Seed Yield of Pea and Lentil

Field experiments were conducted in 2004 and 2005 to determine the effects of seed treatment with Rhizobium leguminosarum bv. viceae on damping‐off, seedling height, root nodule mass, root biomass, shoot biomass and seed yield of pea and lentil in a field naturally infested with Pythium spp. Compared with the untreated controls, treatment of pea seeds with R. leguminosarum bv. viceae strains R12, R20 or R21 significantly (P < 0.05) reduced incidence of damping‐off, promoted seedling growth and increased root nodule mass, root biomass and shoot biomass. Seed treatments with R12 or R21 also resulted in a significant (P < 0.05) increase in seed yield of pea. The strain R21 was most effective among the four strains of R. leguminosarum bv. viceae tested in peas. Although, the level of disease control by strain R21 was similar to seed treatment with the fungicide Thiram^TM, R21 was more effective in enhancing root nodule production and promoting plant growth. For lentil, treatment of seeds with R. leguminosarum bv. viceae strains R12 or R21 significantly (P < 0.05) reduced incidence of damping‐off compared with the untreated control. All of the four strains of R. leguminosarum bv. viceae tested increased lentil seedling height, root nodule mass and shoot biomass, and all except R20 increased root biomass. Seed yield was higher for the treatments of R12 and R21. The strain R12 was most effective among the four strains of R. leguminosarum bv. viceae tested in lentil. Although, strain R12 was as effective as Thiram^TM for control of damping‐off of lentil, it was more effective than Thiram^TM for the production of root nodules and promotion of plant growth. The study concludes that seed treatment with R. leguminosarum bv. viceae is effective in control of Pythium damping‐off of pea and lentil and that the efficacy of control is strain specific, strain R21 for control of the disease on pea and strain R12 for control of the disease on lentil.     

不同产地苦楝苗期生长节律研究

苦楝在我国分布广泛,具有丰富的遗传变异性。为进一步做好苦楝种源筛选和良种选育工作,该文对不同产地苦楝实生苗生长性状和各阶段的生长特点进行了比较分析,初步揭示了苦楝苗期生长规律。以15个产地的1年生实生苗为试材,对苗高、地径、复叶生长及生物量积累等生长性状进行了观测分析,并用Logistics方程对生长节律进行了拟合。结果表明:(1)不同产地苦楝苗高、地径生长差异均达显著水平,根生物量、茎生物量及复叶相关性状差异均达极显著性水平;(2)苗高和地径生长均呈现慢-快-慢的S型生长规律,且均存在2次生长高峰,与苗高生长高峰出现时间相比,地径生长高峰出现时间较晚;(3)Logistic拟合方程的R²为0.976～0.994,均达到极显著相关水平,说明可用Logistic方程拟合苦楝的生长节律;(4)总体上地径速生期较苗高速生期长20～30 d,北方产地苗高和地径进入速生期和结束速生期的时间均早于南方产地,速生期苗高和地径累积生长量均超过总生长量的60%;(5)各生长指标均与纬度负相关,苗高、生物量及复叶面积与经度正相关,其他指标与经度负相关。综上结果表明,苦楝为全期生长型树种,各生长性状在产地间达显著差异水平,生长受纬度和经度双重控制,以纬度控制为主。     

Non‐destructive allometric estimates of above‐ground and below‐ground biomass of high‐mountain vegetation in the Andes

Aim

Studies that monitor high‐mountain vegetation, such as paramo grasslands in the Andes, lack non‐destructive biomass estimation methods. We aimed to develop and apply allometric models for above‐ground, below‐ground and total biomass of paramo plants.

Location

The paramo of southern Colombia between 1°09′N and 077°50′W, at 3,400 and 3,700 m a.s.l.

Methods

We established 61 1‐m² plots at random locations, excluding disturbed, inaccessible and peat bog areas. We measured heights and basal diameters of all vascular plants in these plots and classified them into seven growth forms. Near each plot, we sampled the biomass from plants of abundant genera, after having measured their height and basal diameter. Hence, we measured the biomass of 476 plants (allometric set). For each growth form we applied power‐law functions to develop allometric models of biomass against basal diameter, height, height x basal diameter and height × basal area. The best models were selected using AIC_c weights. Using the observed and predicted plant biomass of the allometric set we calculated absolute percentage errors using cross‐validation. The biomass of a plot was estimated by summing the predicted biomass of all plants in a plot. Confidence limits around these sums were calculated by bootstrapping.

Results

For groups of <20 plants the biomass predictions yielded large (>15%) errors. Applying groups that resembled the 1‐m² plots in density and composition, the errors for above‐ground and total biomass estimates were <15%. Across all plots, we obtained an above‐ground, below‐ground and total plot biomass of 329 ± 190, 743 ± 486 and 1011 ± 627 g/m² (mean ± SD), respectively. These values were within the range of biomass estimates obtained destructively in the tropical Andes.

Conclusions

In new applications, if target vegetation samples are similar regarding growth forms and genera to our allometric set, their biomass might be predicted applying our equations, provided they contain at least 50–100 plants. In other situations, we would recommend gathering additional biomass measurements from local plants to evaluate new regression equations.     

Does decomposition of standard materials differ among grassland patches maintained by livestock?

Grazing can modify vegetation structure and species composition through selective consumption, modifying plant litter quality and hence decomposability. In most grasslands, moderate stocking rates maintain a mosaic of high‐quality patches, preferentially used by herbivores (‘grazing lawns’), and low‐quality tall patches, which are avoided. In grazing lawns decomposition rates can be accelerated because of the higher litter quality of its component species and, besides, through the indirect effect of increased nutrient availability in soil. We aimed at testing this indirect effect using standard materials, comparing their decomposition in grazing lawns, open and closed tall tussock grasslands. We selected 10 patches of each type and sampled floristic composition, soil variables and cattle dung deposition. Standard materials were filter paper and Poa stuckertii litter. We prepared litterbags of 0.3 mm (thin mesh) and 1 mm mesh size (coarse mesh). Samples were incubated for 65 days in two ways: above‐ground (thin and coarse mesh) and below‐ground (only thin mesh), aiming at analysing the conditions for decomposition for surface litter and buried litter or dead roots, respectively. Physical and chemical soil variables did not differ among patch types, despite the differences in species composition. Closed tussock grasslands showed the lowest dung deposition, confirming the less intense use of these patches. Soil nitrogen availability (N‐NO₃^‐ and N‐NH₄⁺) was not significantly different among patch types. Each standard material followed a different decomposition pattern across patch types. For above‐ground incubated samples, Poa litter decomposed significantly faster in lawns, and slower in open tussock grasslands. Filter paper decomposed significantly faster in closed tussock grasslands than in the other two patch types. Decomposition of below‐ground incubated samples did not significantly differ among patch types, in line with results for soil variables. Above‐ground differences in decomposition may be associated with differences in microclimatic conditions resulting from differences in vegetation structure.     

Competition between Lolium perenne and Digitaria sanguinalis: Ecological consequences for harbouring an endosymbiotic fungus

Abstract. This study examined the influence of the fungal endophyte Neotyphodium lolii on the competitive interactions between its perennial, cool season host, Lolium perenne (perennial ryegrass), and a warm season, annual grass, Digitaria sanguinalis (large crabgrass), in densely planted stands (>1000 plant.m^?2) in the glasshouse. Endophyte infection had little or no effect on L. perenne tiller production, above‐ or below‐ground biomass or root: shoot ratio in monoculture. However, endophyte infection significantly reduced L. perenne tiller production and above‐ground biomass in mixtures with D. sanguinalis. Conversely, D. sanguinalis had significantly higher above‐ground biomass and yielded more seed (g) when competing with endophyte infected L. perenne. An apparent trade‐off between allocation of resources to reproductive vs root tissues was observed in D. sanguinalis– root: shoot ratio was significantly lower when competing with endophyte infected L. perenne. Results indicate negative ecological consequences for harbouring the fungal endophyte when competing with the fast growing annual grass in newly established stands. These findings underscore the existence of a physiological cost of harbouring the fungal endophyte which is often overlooked.     

Differential recovery of above‐ and below‐ground rich fen vegetation following fertilization

Abstract. For seven years we studied the recovery of vegetation in a Belgian P limited rich fen (Caricion davallianae), which had been fertilized with nitrogen (200 g.m^?2) and phosphorus (50 g.m^?2) in 1992. The vegetation in this fen has low above‐ground biomass production (< 100 g m^?2) due to the strong P limitation. Above‐ground biomass was harvested from 1992 to 1998 and P and N concentrations measured. In 1998, below‐ground biomass was also harvested. The response to fertilization differed markedly between below‐ and above‐ground compartments. Above‐ground, P was the single most important factor that continued to stimulate growth 7 yr after fertilization. Below‐ground, N tended to decrease live root biomass and increase dead root biomass and seemed to have a toxic effect on the roots. In the combined NP treatment the stimulating effect of P (an increase of live root biomass) was countered by N. The 1998 soil analysis showed no difference in soil P in the plots. Thus, Fe hydroxides are not capable of retaining P in competition with fen vegetation uptake. However, higher capture of P in root Fe coatings from N plots may partially explain this negative N effect. The results suggest that N root toxicity will be amplified in strongly P limited habitats but that its persistence will be less influenced by P availability. This mechanism may be a competitive advantage for N₂ fixing species that grow in strongly P limited wetlands.