Decreased root heterogeneity and increased root length following grassland invasion

Abstract

Summary1. Plant invasions can be promoted by environmental heterogeneity, but the opposite effect, the impact of plant invasion on heterogeneity, has received little attention. Grassland invasions might contribute to decreased spatial heterogeneity because invaders tend to be larger than native vegetation. Lowered heterogeneity may contribute to the low diversity of invaded communities, as well as to the persistence of invasive populations. 2. We compared the spatial heterogeneity of roots and resources in uninvaded native grassland and in stands invaded by a relatively large exotic grass (Agropyron cristatum), in four combinations of mowing and nitrogen (N) addition. We focused on roots because they account for the majority of primary production in grasslands. 3. The spatial heterogeneity of root length (m root m À2 rhizotron image) and root production was significantly lower beneath A. cristatum than uninvaded grassland. This result was consistent in all combinations of mowing and N addition. 4. Beneath the invader, root length was significantly greater, and the proportion of samples that contained roots was significantly higher. This suggests that the invader decreased spatial heterogeneity by more completely filling the soil volume with roots. 5. Resource heterogeneity varied significantly between vegetation types in just one of four cases examined, suggesting that invader effects on resource heterogeneity were small relative to its effects on root heterogeneity. 6. These results suggest a novel mechanism promoting invader success and persistence: high root heterogeneity, lower root length and empty soil volumes in native grassland may make it relatively vulnerable to invasion, while reduced heterogeneity and greater root length in invaded grasslands may sustain stable, low-diversity communities dominated by the invader. Lowered heterogeneity accompanying invasion may partly account for the wide-spread occurrence of low-diversity, invader-dominated grasslands in North America.

Belowground plant functional ecology: Towards an integrated perspective

“…Nevertheless, thanks to recent progresses in molecular techniques, this problem has become increasingly solvable even for herbaceous communities (Herben et al., ; Hiiesalu et al., ; Mommer, Wagemaker, de Kroon, & Ouborg, ). A consequence of the coring procedure is the fragmentation of belowground organs so that information on their position (in relation to the original location of different organs belowground) is lost during the sampling process (Larreguy, Carrera, & Bertiller, ; Vaness, Wilson, & MacDougall, ). As soil‐core sampling is an unavoidably destructive procedure, issues remain whether the research targets to obtain time‐series data, such as biomass allocation over time.…”

Root heterogeneity along an arctic elevational gradient: the importance of resolution

“…The presence of many empty cells (i.e. RLD = 0), however, can influence CV (Vaness, Wilson & MacDougall ) of our tested resolutions. We examined this possibility in three ways.…”

Seasonal Salinization Decreases Spatial Heterogeneity of Sulfate Reducing Activity

“…Previously, this method has been used to document the presence or absence of reducing conditions or broadly characterize SO 4 2− reduction [24,26], but has not yet been used to identify individual complex size or area, or quantify the spatial patterns within these complexes. Spatial patterns, however, have previously been documented in regards to soil nitrogen presence as well as denitrification activity [28,29], plant root presence [30], soil carbon [31], and soil fertility [30]. Our modification of the IRIS technique results in a high-resolution image of in situ FeS precipitation dynamics in a sediment and some new metrics associated with FeS quantification by capturing a view of the microbial and mineralogical activity of a sediment at the scale at which it occurs.…”