Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors.Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past,our understanding of it remains limited.This is because the dynamics processes associated with soil resources availability are still poorly understood.Soil moisture,temperature,and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level.In temperate forest ecosystems,seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground.Therefore,fine root biomass,root length density(RLD)and specific root length(SRL)vary during the growing season.Studying seasonal changes of fine root biomass,RLD,and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover.The objective of this study was to understand whether seasonal variations of fine root biomass,RLD and SRL were associated with soil resource availability,such as moisture,temperature,and nitrogen,and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation.We used a soil coring method to obtain fine root samples(≤2 mm in diameter)every month from May to October in 2002 from a 17-year-old L.gmelinii plantation in Maoershan Experiment Station,Northeast Forestry University,China.Seventy-two soil cores(inside diameter 60 mm;depth intervals:0-10 cm,10-20 cm,20-30 cm)were sampled randomly from three replicates 25 m×30 m plots to estimate fine root biomass(live and dead),and calculate RLD and SRL.Soil moisture,temperature,and nitrogen(ammonia and nitrates)at three depth intervals were also analyzed in these plots.Results showed that the average standing fine root biomass(live and dead)was 189.1 g·m^(-2)·a^(-1),50%(95.4 g·m^(-2)·a^(-1))in the surface soil layer(0-10 cm),33%(61.5 g·m^(-2)·a^(-1)),17%(32.2 g·m^(-2)·a^(-1))in the middle(10-20 cm)and deep layer(20-30cm),respectively.Live and dead fine root biomass was the highest from May to July and in September,but lower in August and October.The live fine root biomass decreased and dead biomass increased during the growing season.Mean RLD(7,411.56 m·m^(-3)·a^(-1))and SRL(10.83 m·g^(-1)·a^(-1))in the surface layer were higher than RLD(1474.68 m·m^(-3)·a^(-1))and SRL(8.56 m·g^(-1)·a^(-1))in the deep soil layer.RLD and SRL in May were the highest(10621.45 m·m^(-3) and 14.83m·g^(-1))compared with those in the other months,and RLD was the lowest in September(2198.20 m·m^(-3))and SRL in October(3.77 m·g^(-1)).Seasonal dynamics of fine root biomass,RLD,and SRL showed a close relationship with changes in soil moisture,temperature,and nitrogen availability.To a lesser extent,the temperature could be determined by regression analysis.Fine roots in the upper soil layer have a function of absorbing moisture and nutrients,while the main function of deeper soil may be moisture uptake rather than nutrient acquisition.Therefore,carbon allocation to roots in the upper soil layer and deeper soil layer was different.Multiple regression analysis showed that variation in soil resource availability could explain 71-73%of the seasonal variation of RLD and SRL and 58%of the variation in fine root biomass.These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability,which resulted in an increased allocation of carbohydrate to these roots,but a lower allocation of carbohydrate to those in soil with lower resource availability.

Response of root traits of Reaumuria soongorica and Salsola passerina to facilitation

C3 plant Reaumuria soongorica and C4 plant Salsola passerina are super xerophytes and coexist in a mixed community in either isolated or associated growth, and interspecific facilitation occurs in associated growth. In the present study, the root traits including root distribution, root length（RL）, root surface area（RSA）, root weight（RW） and specific root length（SRL） of both species in two growth forms were investigated to clarify their response to facilitation in associated growth. Six isolated plants of each species, as well as six associated plants similar in size and development were selected during the plant growing season, and their roots were excavated at 0–10, 10–20, 20–30, 30–40 and 40–50 cm soil depths at the end of the growing season. All the roots of each plant were separated into the two categories of fine roots（2 mm diameter） and coarse roots（≥2 mm diameter）. Root traits such as RL and RSA in the fine and coarse roots were obtained by the root analyzing system WinRHIZO. Most of the coarse roots in R. soongorica and S. passerina were distributed in the top 10 cm of the soil in both growth forms, whereas the fine roots of the two plant species were found mainly in the 10–20 and 20–30 cm soil depths in isolated growth, respectively. However, the fine roots of both species were mostly overlapped in 10–20 cm soil depth in associated growth. The root/canopy ratios of both species reduced, whereas the ratios of their fine roots to coarse roots in RL increased, and both species had an increased SRL in the fine roots in associated growth. In addition, there was the increase in RL of fine roots and content of root N for S. passerina in associated growth. Taken together, the root growth of S. passerina was facilitated for water and nutrient exploration under the interaction of the overlapped roots in both species in associated growth, and higher SRL allowed both species to more effectively adapt to the infertile soil in the desert ecosystem.

Evaluation of Tropical Legume Cover Crops for Copper Use Efficiency

Cover crops are important components of cropping systems due to their role in improving soil quality. Lack of adequate levels of soil micronutrients prevents the success of cover crops in highly weathered tropical soils. A greenhouse experiment was conducted with the objective to evaluate copper use efficiency of nine tropical legume cover crops. The copper levels used were 0, 5, 10 and 20 mg Cu kg-1 of soil. Shoot dry weight, maximum root length and root dry weight significantly increased in a quadratic fashion with increasing soil Cu levels in the range of 0 to 20 mg kg-1 soil. Cu x cover crops interactions for shoot dry weight, root dry weight, maximum root length and contribution of root to the total dry weight were significant, indicating different responses of cover crops with the variation in soil Cu levels. Overall, maximum shoot dry weight was obtained with the application of 13 mg Cu kg-1. Similarly, maximum root dry weight and maximum root length were obtained with the application of 12 and 14 mg Cu kg-1 of soil. Root dry weight and maximum root length were significantly and positively related to shoot dry weight, indicating that a vigorous root system is important for improving productivity of cover crops grown on Brazilian Oxisols, especially where deficiency of micronutrients such as Cu exists. The Cu concentration in the plant tissue decreased in a quadratic fashion whereas, Cu uptake increased with increasing Cu application rate from 0 to 20 mg kg-1 soil. There was a significant variation observed in Cu use efficiency among cover crop species. Increasing applied Cu levels significantly increased soil pH and Mehlich 1 extractable soil Cu, Zn, Mn and Fe concentrations in the soil solution.

Closely related allopatric Podalyria species from the Core Cape Subregion differ in their mechanisms for acquisition of phosphorus,growth and ecological niche

Aims In the Core Cape Subregion(CCR),a Mediterranean-climate ecosystem with infertile soils,the legume species Podalyria calyptrata and P.burchellii are in a separate clade to P.leipoldtii and P.myrtillifolia.The closely related species are allopatric,and with the west-east climate gradient and variation in soil nutrient availability in the CCR,it was hypothesized that the two closely related allopatric species would differ in their ecological niche and root:shoot ratio,specific root length(SRL)and organic acid exudation responses to phosphorus(P)supply.Methods With increasing P supply in the glasshouse,we measured plant biomass,leaf nitrogen([N]),[P],root morphology and release of organic acids.We determined species soil and leaf[N]and[P]and climate in field sites.Important FindingsAt low P supply,P.calyptrata roots exuded more organic acids than P.burchellii which instead produced roots with a greater SRL,and P.myrtillifolia allocated more biomass to roots than P.leipoldtii.In the field,leaf[P]and climate suggested that P.leipoldtii occupied the most oligotrophic niche followed by P.burchellii and then P.calyptrata and P.myrtillifolia.Closely related allopatric species differed in their mechanisms for P-acquisition and ecological niche,indicating that the environment overrides phylogeny in determining P-acquisition traits for these species,and suggesting that climate regulates nutrient availability,driving distribution and speciation.