Plant-to-plant direct competition for belowground resource in an overlapping depletion zone

In response to limited availability of soil resources in basal root zone, plant extends its roots into nearby resource-rich zones to fulfill essential resource demands for survival and reproduction. This root proliferation into that enriched zones occupied by other plants constitutes interplant overlapping rooting zones and thereby the overlapping depletion zones, causing reduction in resource uptake by neighboring plants. By incorporating this mechanism into the classic resource competition model, we study interplant direct competition through their rooting system in an overlapping depletion zone. The model results indicate an extension of Tilman’s R* rule that has already been proved true when plants compete indirectly through their effect on shared resources. The results reveal that plant’s direct competitive ability (i.e., the ability to occupy an overlapping depletion zone by excluding others) can be characterized by its R*-value, where a best competitor having lowest R*-value excludes others from an overlapping zone and occupies the zone by depleting the resource level to the lowest as in its non-overlapping depletion zone. By analyzing the model, we find a suite of traits that confers R* variation among directly competing plants. This suite of traits would be a useful proxy measure for R* that do not necessarily require to establish equilibrium field monoculture—a requirement for R* measurement in the field.

Temperature-water and competitive interactions in vitro of two toxic black molds,Fusarium oxysporum and Rhizopus stolonifer isolated from a shower setting

We report differences in secondary resource capture and upper lethal temperature as survival attributes for Fusarium oxysporum(FOSC)and Rhizopus stolonifer,two medically important fungi that were co-isolated from a table shower caddy.Isolates of these two shower-associated fungi have been deposited at the University of Alberta Microfungus Collection and Herbarium,Centre for Global Microfungal Biodiversity(UAMH,Toronto,CAN)as R.stolonifer UAMH 11965 and F.oxysporum(FOSC)UAMH 11966;this paper provides growth characteristics for these two strains that can be used for further studies on black molds in bathrooms given the relevance to public health.Both R.stolonifer UAMH 11965 and F.oxysporum(FOSC)UAMH 11966 require contact with a wet surface substrate with water activity≥0.95 aw for growth and sporulation.In contrast to F.oxysporum,R.stolonifer has a 4-6x,faster radial growth rate,superior colonizing ability,and capacity for overgrowth(exploitative competition).This F.oxysporum(FOSC)strain,however,is thermotolerant,as demonstrated by broader thermal growth range and higher optimum temperature,which puts fewer limitations on its growth compared to R.stolonifer.This is a point of public awareness for mold-sensitive and immunocompromised people that wet,wood substrates in a shower can permit colonization and competitive interactions that can concentrate R.stolonifer and F.oxysporum spores.

Genotype and Planting Density Effects on Rooting Traits and Yield in Cotton （Gossypium hirsutum L,）

Root density distribution of plants is a major Indicator of competition between plants and determines resource capture from the solh This experiment was conducted in 2005 at Anyang, located in the Yellow River region, Henan Province, China. Three cotton （Gossyplum hlrsutum L.） cultivars were chosen： hybrid Btcultlvar CRI46, conventional Btcultlvars CRI44 and CRI45. Six planting densities were designed, ranging from 1.5 to 12.0 plants/m^2. Root parameters such as surface area, diameter and length were analyzed by using the DT-SCAN Image analysis method. The root length density （RLD）, root average diameter and root area Index （RAI）, root surface area per unit land area, were studied. The results showed that RLD and RAI differed between genotypes; hybrid CRI46 had significantly higher （P 〈0.05） RLD and RAI values than conventlonal cultlvars, especially under low planting densities, less than 3.0 plants/m^2. The root area index （RAI） of hybrid CRI46 was 61% higher than of CRI44 and CRI45 at the flowering stage. The RLD and RAI were also significantly different （P = 0.000） between planting densities. The depth distribution of RAI showed that at Increasing planting densities RAI was Increasingly distributed in the soil layers below 50 cm. The RAI of hybrid CRI46 was for all planting densities, obviously higher than other cultivars during the flowering and boll stages. It was concluded that the hybrid had a strong advantage in root maintenance preventing premature senescence of roots. The root diameter of hybrid CRI46 had a genetically higher root diameter at planting densities lower than 6.0 plants/m^2. Good associations were found between yield and RAI In different stages. The optimum planting density ranged from 4.50 plants/m^2 to 6.75 plants/m^2 for conventional cultlvars and around 4.0-5.0 plants/m^2 for hybrids.