Reaction kinetics of poikilotherm development.

Soil temperature can influence the functioning of roots in many ways. If soil moisture and nutrient availability are adequate, rates of root length extension and root mortality increase with increasing soil temperature, at least up to an optimal temperature for root growth, which seems to vary among taxa. Root growth and root mortality are highly seasonal in perennial plants, with a flush of growth in spring and significant mortality in the fall. At present we do not understand whether root growth phenology responds to the same temperature cues that are known to control shoot growth. We also do not understand whether the flush of root growth in the spring depends on the utilization of stored nonstructural carbohydrates, or if it is fueled by current photosynthate. Root respiration increases exponentially with temperature, but Q10 values range widely from c. 1.5 to > 3.0. Significant questions yet to be resolved are: whether rates of root respiration acclimate to soil temperature, and what mechanisms control acclimation if it occurs. Limited data suggest that fine roots depend heavily on the import of new carbon (C) from the canopy during the growing season. We hypothesize that root growth and root respiration are tightly linked to whole-canopy assimilation through complex source–sink relationships within the plant. Our understanding of how the whole plant responds to dynamic changes in soil temperature, moisture and nutrient availability is poor, even though it is well known that multiple growth-limiting resources change simultaneously through time during a typical growing season. We review the interactions between soil temperature and other growth-limiting factors to illustrate how simple generalizations about temperature and root functioning can be misleading.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2000.00689.x

Responses of tree fine roots to temperature

Growth Rates and Growth Periodicity of Tree Roots

Phenology has been defined as the study of the timing of recurring biological events, the causes of their timing with regard to abiotic and biotic forces and the interrela tion among phases of the same or different event (Reichle 1973, Leith 1974). The role of phenology in forest eco systems has been discussed for several decades. Today, understanding how tree phenology is quantitatively re lated to environment is even more important because of anticipated global environmental change. One of the first steps in modeling tree growth is to define climatic conditions under which growth initiates and ceases. Increased ambient temperatures can be ex pected to change growth patterns through effects on plant processes such as dormancy deepening, cold hardiness and dormancy release. Modeling the phenology of pines under current and altered climates may not be easy be cause of their wide geographic and climatic range and the diversity of genotypes that have evolved. We have selected to review the phenology of six con trasting species of pine: Pinus radiata D. Don (Monterey pine), P. taeda L. (loblolly pine), P. strobus L. (eastern white pine), P. elliottii Engelm. (slash pine), P. contorta Doug. ex. Loud, (lodgepole pine), and P. sylvestris L. (Scots pine). The specific emphasis is on interactions between environment and tree morphology, anatomy and physiology and how these interactions affect patterns of tree growth and stand productivity. The phenophases to be considered are: shoot growth, stem diameter growth, foliage and branch production and root growth. Com ments on other phenophases will be made where they appear to have major, short duration impacts on the growth activities being considered.

Environmental influences on the phenology of pine

SUMMARY
The effects of photon irradiance on the growth of young plants (up to three weeks old) of Trifolium subterraneum L. and on the development of mycorrhizal root systems were studied with plants grown in a soil/sand mixture inoculated with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe. Total plant growth was lower when photon irradiance was 100 μmol m−2 s−1, compared with 450 μmol m−2 s−1. Fresh weight of shoots was unaffected, but the fresh weight/dry weight ratio was increased at the lower irradiance in shoots, but not in roots. The main effect of decreased irradiance on the growth of the root system was a reduction in the numbers of first- and second-order lateral roots initiated. The average rate of extension of axial and lateral roots was only slightly reduced. The fraction of the root length infected was lower at the lower irradiance, particularly in the first two weeks. Development of infection was analyzed in terms of the role of formation of mycorrhizal entry-points (A) and the average rate of growth of infection units (B). Reduction in the fraction of the root length infected was found to be due to a reduction in A. B was remarkably constant at the two irradiances and in the different root subsystems. Thus both roots and infection units respond by making fewer units of unaltered rate of growth.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1986.tb00623.x

Effects of photon irradiance on the growth of shoots and roots, on the rate of initiation of mycorrhizal infection and on the growth of infection units in Trifolium subterraneum L.

made under controlled conditions. Reed noted a marked reduction in root growth during the time when soil temperatures were lowest and also at times when the soil was driest. Turner's data also indicate this same general trend. It was, therefore, decided to measure root growth of loblolly pine under controlled conditions to find whether or not a definite and perhaps quantitative relationship to soil temperature and other factors could be shown. Materials and methods Two series of experiments were performed, the first during the spring and summer of 1941, the second during the winter of 1946. The seedlings need in 1941 were grown from seed collected in North Carolina in 1940, and the seedlings used in 1946 were grown from seed collected in Louisiana in 1945. The seedlings were grown in glass tubes about two inches in diameter and 18 inches long. These tubes were closed at the lower end with rubber stoppers and a layer of cinders placed over the stoppers. The tubes were then filled with a loamy greenhouse soil, which was kept wetted to field capacity. Although the soil was heated in an electric sterilizer before use, it still contained two species of small animals, a nematode and a collembolan. Neither seemed to be harmful; apparently they fed only on dead tissue sloughing off the roots. The collembolans may have aided in aeration by opening small passageways in the soil. The soil atmosphere in the tubes was analyzed with a Haldane apparatus and found to have approximately the same concentration of oxygen as the outside air. The concentration of carbon dioxide in the soil was somewhat higher than outside. The average amount was 1.0% and the maximum 2.88%. Cannon and Free (?) reported that for several species there was no detrimental effect on root growth of 20% or more carbon dioxide if oxygen were not deficient. Since the soil atmosphere normally contains more carbon dioxide than ordinary atmosphere and excesses from 0.2 to 5% are not unusual (28), it is believed that growth was not abnormally influenced by deficient oxygen or by an excess of carbon dioxide. 146

Effects of soil temperature and light intensity on root growth of loblolly pine seedlings

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Effects of soil temperature and light intensity on root growth of loblolly pine seedlings