No abstract

The root electrical capacitance (CR) method is suitable for assessing root growth and activity, but soil water content (SWC) strongly influences the measurement results. This study aimed to adapt the method for field monitoring by evaluating the effect of SWC on root capacitance to ensure the comparability of CR detected at different SWC. First a pot experiment was conducted with maize and soybean to establish CR–SWC functions for the field soil. Ontogenetic changes in root activity were monitored under field conditions by simultaneously measuring CR and SWC around the roots. The CR values were normalized using SWC data and experimental CR–SWC functions to obtain CR*, the comparable indicator of root activity. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on the CR* and biomass of field-grown soybean was investigated. The pot trial showed an exponential increase in CR with SWC. CR–SWC functions proved to be species-specific. CR showed strong correlation with root dry mass (R2 = 0.83–0.87). The root activity (CR*) of field-grown crops increased until flowering, then decreased during maturity. This was consistent with data obtained with other methods. AMF inoculation of soybean resulted in significantly higher CR* during the late vegetative and early flowering stages, when destructive sampling concurrently showed higher shoot biomass. The results demonstrated that the root capacitance method could be useful for time course studies on root activity under field conditions, and for comparing single-time capacitance data collected in areas with heterogeneous soil water status.

Invasion of alien plant species is one of the main reasons for biodiversity loss in terrestrial ecosystems. However, alien plant species are not evenly distributed in the landscape. We studied which factors determine the actual level of neophyte invasion in a landscape with heterogeneous land-use and which habitats are the most infected. Since neophyte species with different life-forms can respond differently to the factors determining the invasion, species groups of annual, herbaceous perennial and woody neophytes were also analyzed separately. The study was conducted within the field site network of the Kiskun-LTER program (Hungary), in 16 sites of 5 km  5 km. Fifteen habitat types were distinguished belonging to five major land-use/land cover types (agricultural land, abandoned agricultural land, tree plantation, semi-natural grassland and semi-natural forest). Present and past land-use, landscape composition and environmental variables were included as factors with a potential impact on the level of invasion. The most important factor determining invasion level was present habitat type, followed by the past habitat type of the location and landscape context. Tree plantations, agricultural habitats and recently abandoned agricultural habitats had the highest level of invasion. As expected, annual neophytes were most abundant in agricultural habitats, while perennial herbaceous neophytes were most abundant in old-fields and plantations, and woody neophytes in tree plantations. Past agricultural land-use was reflected in the higher levels of invasion of annuals and perennials, and past forestry practice resulted in higher levels of invasion of woody neophytes. In a landscape with a higher proportion of tree plantations, not only the tree plantations, but primary woodland [ 2 4 0 _ T D $ D I F F ] patches also showed higher levels of invasion by woody neophyte species. Our results indicate the importance of present and past land-use in plant invasion and suggest that tree plantations are hot-spots of plant invasion and threaten the remnants of semi-natural vegetation.