Studies on seedling growth of temperate and tropical trees

Abstract

The investigations here reported were designed to study the comparative physiological characteristics of Quercus robur, Betula pendula seedlings as influenced by aspects of soil and light environments. A comparative soil type experiment using a tropical fast-growing tree (Terminalia ivorensis) in addition to the temperate trees was also possible.

These experiments were set up to explore the limiting factors responsible for failure of natural regeneration. The first experiment involved using an artificial growing medium (peralite) fed with different types of culture solutions for the growth of the seedlings. The role of nitrogen, phosphorus, and complete absence of nutrients on seedlings was examined. Q. robur was more sensitive to nitrogen deficiency than to that of phosphorus. Q. robur seedlings performed similarly in absence of phosphorus and in complete presence of nutrients. B. pendula seedlings on the other hand were seriously affected by the deficiency of both elements and phosphorus seemed more important than nitrogen to B. pendula seedling growth.

Chemical analyses showed evidence of nitrogen deficiency in both species. In Q. robur phosphorus did not show any marked inbalance. B. pendula seedlings in a number of treatments were too small for any detailed analysis. The chemical analyses also confirmed the acorn as a main source of nutrient supply of young seedlings of Q. robur. Dry matter yield of Q. robur was not affected by soil volume variation, while B. pendula seedlings had growth performances almost proportional to the soil volume available. An attempt to distinguish the separate effects of mechanical impendance and aeration gave no clear-cut result.

The soil type experiment was designed to investigate the role of soil factors on the seedling growth of Q. robur, B. pendula and T. ivorensis. Only B. pendula seemed able to grow on a calcareous soil, robur did not produce new shoots at all, while a number of T. ivorensis seedlings died on this calcareous soil. The growth of all seedlings on two other soil types (acidic) was relatively poor. These soils were generally poor in major soil nutrients especially nitrogen, phosphorus and potassium. The fourth soil type from under a rich mixture of B. pendula and Q. robur trees produced good growth of seedlings generally. The soil was rich in the major soil elements. The analysis of plant growth showed that the three species were affected by ontogenetic drift.

B. pendula had the highest relative growth rates in all soil types, and Q. robur the least. Due to the nature of the different soils, the relative growth rates of the seedlings were markedly affected. On the calcareous soil, Q. robur and T. ivorensis showed no dry weight increase after transplanting. On the soil type IV the species had high growth rates which fell with time. These results indicate that soil factors may affect the distribution of Q. robur and B. pendula, although other factors were also thought to interact with soil nutrients.

The effects of shade and fertilizer on the seedling growth of Q. robur and B. pendula was investigated by growing these seedlings in shaded enclosures providing 30%, 10% and 5% approximately of total daylight. The soil condition on which the seedlings were growing vas also varied by growing some seedlings in ordinary garden soil and others in garden soil mixed with a level of John Innes fertilizer. Q. robur was not influenced by the fertilizer treatment. The fertilizer addition was significant to the B. pendula seedling only in the 20% light and only towards the end of the season. The fertilizer effect was also thought to have increased the susceptibility of B. pendula seedlings to fungal attack in the light. B. pendula showed adaptation to shading by increasing specific leaf area.

The experiment on various degrees of shading on B. pendula seedlings previously grown in 100% daylight helped to clarify some points about this species under shade. The results of the specific leaf area values increasing with shade confirms the fact that B. pendula might probably withstand some shading if for example it was able to put up some growth under a temporarily open canopy. The results also indicate the fact that B. pendula would respond favourably to fertilizer application at this seedling stage, if the light condition is adequate. The performance of B. pendula seedlings in 25% and 85% daylight were quite comparable.

In conclusion, it was believed that light was the major important factor of the environment affecting natural regeneration of Q. robur and B. pendula seedlings in British semi-natural forests, except in certain types of soils, for example on certain calcareous soils. Further studies on these seedlings especially in relation to their herbaceous competitors was recommended. (Abstract shortened by ProQuest.)