Diversity effects on root length production and loss in an experimental grassland community
Mommer, L. ; Padilla, F.M. ; Ruijven, J. van; Caluwe, H. de; Smit-Tiekstra, A.E. ; Berendse, F. ; Kroon, H. de - \ 2015
Functional Ecology 29 (2015)12. - ISSN 0269-8463 - p. 1560 - 1568.
1.Advances in root ecology have revealed that root standing biomass is higher in species-rich plant communities than in species-poor communities. Currently, we do not know whether this below-ground diversity effect is the result of enhanced root production or reduced root mortality or both, which is essential information to understand ecosystem functioning, as it determines C sequestration and N dynamics in soil. 2.Minirhizotron observations were combined with root coring in five different plant communities (four monocultures and the respective mixture). Molecular markers were used to quantitatively determine species abundance in mixed root biomass samples in order to track shifts in below-ground species composition. In addition, a litterbag experiment was performed to study root decomposition independent of root mortality. 3.Root length production was greater and root length loss was lower in the mixture than expected from monocultures in all years. Simulations suggest that at least two species must have had reduced losses in mixture compared to monoculture. However, the diversity effects on root mortality may partially be explained by selection effects as the species with the longest root life span became dominant in the mixtures. Root length loss from minirhizotrons was very low; the combination of minirhizotron length measurements with root biomass estimates from coring suggested underestimation of root loss in minirhizotrons over time. Root decomposition was not affected by diversity. 4.Diversity enhanced root length production and decreased root loss, resulting in below-ground overyielding. With decomposition unaffected, our results suggest that root mortality is reduced with increasing diversity. Future studies have to reveal the generality of our observations in larger scale biodiversity experiments by using species having a wider variety of root traits.
Spatial heterogeneity of plant–soil feedback affects root interactions and interspecific competition
Hendriks, M. ; Ravenek, J. ; Smit-Tiekstra, A.E. ; Paauw, J.W.M. van der; Caluwe, H. de; Putten, W.H. van der; Kroon, H. de; Mommer, L. - \ 2015
New Phytologist 207 (2015)3. - ISSN 0028-646X - p. 830 - 840.
nutrient heterogeneity - species-diversity - population-dynamics - relative abundance - deciduous woodland - temporal variation - borne pathogens - grassland - community - coexistence
Plant-soil feedback is receiving increasing interest as a factor influencing plant competition and species coexistence in grasslands. However, we do not know how spatial distribution of plant-soil feedback affects plant below-ground interactions. We investigated the way in which spatial heterogeneity of soil biota affects competitive interactions in grassland plant species. We performed a pairwise competition experiment combined with heterogeneous distribution of soil biota using four grassland plant species and their soil biota. Patches were applied as quadrants of 'own' and 'foreign' soils from all plant species in all pairwise combinations. To evaluate interspecific root responses, species-specific root biomass was quantified using real-time PCR. All plant species suffered negative soil feedback, but strength was species-specific, reflected by a decrease in root growth in own compared with foreign soil. Reduction in root growth in own patches by the superior plant competitor provided opportunities for inferior competitors to increase root biomass in these patches. These patterns did not cascade into above-ground effects during our experiment. We show that root distributions can be determined by spatial heterogeneity of soil biota, affecting plant below-ground competitive interactions. Thus, spatial heterogeneity of soil biota may contribute to plant species coexistence in species-rich grasslands.
Root responses of grassland species to spatial heterogeneity of plant–soil feedback
Hendriks, M. ; Visser, E.J.W. ; Visschers, I.S.G. ; Aarts, B.H.J. ; Caluwe, H. de; Smit-Tiekstra, A.E. ; Putten, W.H. van der; Kroon, H. de; Mommer, L. - \ 2015
Functional Ecology 29 (2015)2. - ISSN 0269-8463 - p. 177 - 186.
nutrient heterogeneity - temporal variation - individual plants - community - growth - plasticity - diversity - availability - succession - microbes
Plant roots selectively forage for soil nutrients when these are heterogeneously distributed. In turn, effects of plant roots on biotic and abiotic conditions in the soil, which result in so-called plant–soil feedback can be heterogeneously distributed as well, but it is unknown how this heterogeneity affects root distribution, nutrient uptake and plant biomass production. Here, we investigate plant root distribution patterns as influenced by spatial heterogeneity of plant–soil feedback in soil and quantify consequences for plant nitrogen uptake and biomass production. We conditioned soils by four grassland plant species to obtain ‘own’ and ‘foreign’ soils that differed in biotic conditions similar as is done by the first phase of plant–soil feedback experiments. We used these conditioned soils to create heterogeneous (one patch of own and three patches of foreign soils) or homogeneous substrates where own and foreign soils were mixed. We also included sterilized soil to study the effect of excluding soil biota, such as pathogens, symbionts and decomposers. We supplied 15N as tracer to measure nutrient uptake. In nonsterile conditions, most plant species produced more biomass in heterogeneous than in homogeneous soil. Root biomass and 15N uptake rates were higher in foreign than own soil patches. These differences between heterogeneous and homogeneous soil disappeared when soil was sterilized, suggesting that the effects in nonsterilized soils were due to species-specific soil biota that had responded to soil conditioning. We conclude that plants produce more biomass when own and foreign soils are patchily distributed than when mixed. We show that this enhanced productivity is due to nutrient uptake being overall most efficient when own and foreign soils are spatially separated. We propose that spatial heterogeneity of negative plant–soil feedback in species diverse plant communities may provide a better explanation of overyielding than assuming that plant–soil feedback effects are diluted.
Early root overproduction not triggered by nutrients decisive for competitive success belowground
Padilla, F.M. ; Mommer, L. ; Caluwe, H. de; Smit-Tiekstra, A.E. ; Wagemaker, C.A.M. ; Ouborg, N.J. ; Kroon, H. de - \ 2013
PLoS ONE 8 (2013)1. - ISSN 1932-6203 - 9 p.
interspecific competition - plant diversity - niche differentiation - negative feedback - species-diversity - seed yield - productivity - communities - maintenance - mechanisms
Background - Theory predicts that plant species win competition for a shared resource by more quickly preempting the resource in hotspots and by depleting resource levels to lower concentrations than its competitors. Competition in natural grasslands largely occurs belowground, but information regarding root interactions is limited, as molecular methods quantifying species abundance belowground have only recently become available. Principal Findings - In monoculture, the grass Festuca rubra had higher root densities and a faster rate of soil nitrate depletion than Plantago lanceolata, projecting the first as a better competitor for nutrients. However, Festuca lost in competition with Plantago. Plantago not only replaced the lower root mass of its competitor, but strongly overproduced roots: with only half of the plants in mixture than in monoculture, Plantago root densities in mixture were similar or higher than those in its monocultures. These responses occurred equally in a nutrient-rich and nutrient-poor soil layer, and commenced immediately at the start of the experiment when root densities were still low and soil nutrient concentrations high. Conclusions/Significance - Our results suggest that species may achieve competitive superiority for nutrients by root growth stimulation prior to nutrient depletion, induced by the presence of a competitor species, rather than by a better ability to compete for nutrients per se. The root overproduction by which interspecific neighbors are suppressed independent of nutrient acquisition is consistent with predictions from game theory. Our results emphasize that root competition may be driven by other mechanisms than is currently assumed. The long-term consequences of these mechanisms for community dynamics are discussed.
Independent variations of plant and soil mixtures reveal soil feedback effects on plant community overyielding
Hendriks, M. ; Mommer, L. ; Caluwe, H. de; Smit-Tiekstra, A.E. ; Putten, W.H. van der; Kroon, H. de - \ 2013
Journal of Ecology 101 (2013)2. - ISSN 0022-0477 - p. 287 - 297.
diversity-productivity relationships - grassland experiment - species coexistence - biodiversity - rhizosphere - competition - mechanisms - succession - dynamics
1. Recent studies have shown that the positive relationship between plant diversity and plant biomass ('overyielding') can be explained by soil pathogens depressing productivity more in low than in high diverse plant communities. However, tests of such soil effects in field studies were constrained by experimental limitations to manipulate soil community composition independent of plant community composition. Here, we report of an experiment where feedback effects to plants were tested for both plant and soil monocultures and mixtures. 2. Our results demonstrate that overyielding is the result of plant species in mixture being more growth-limited by 'own' soil biota than by soil biota of other plant species. This effect disappeared when the soils had been sterilized by gamma-irradiation. Mixing plants themselves did not result in overyielding except when grown in the soil of one of the species (Leucanthemum vulgare), where growth of one species disproportionally increased in mixture compared to monoculture. 3. Soil nutrient availability could not explain differences in growth between the non-sterilized soils. Therefore, our results suggest that plant species-specific soil biota rather than the plants have contributed to the plant community overyielding. 4. Species biomass ranking in mixtures highly differed between non-sterilized soils of different histories of soil conditioning, whilst the ranking was more consistent in sterilized soil. Sterilized soils of different origin differed significantly in nutrient availability. These results suggest that shifts in competitive hierarchies depend on plant species-specific interactions influenced by soil biota and cannot be induced by mineral nitrogen. 5. Synthesis. Our results show that overyielding in four plant species mixtures can be due to species-specific interactions between plants and their specific soil biota. Neither mixing the plant species alone nor the differential responses of species to mineral nitrogen influenced community productivity, but mixing soil biota did.