Broader leaves provide much higher surface area to trap the incident light for photosynthesis than leaves of taller trees...and hence , productivity and rate of photosynthesis are more in trees having broader leaves...

It depends on the habitat- coniferous and broadleaved trees have different adaptations to environmental conditions such as nutrient, water and light availability. Compact needle leaves, for example, minimise water loss and facilitate survival in low moisture habitats, whether that is a warm dry summer or a frozen winter, and can allow a longer photosynthetic season than broad leaves in some habitats. In much of northern Europe spruce has been the favoured choice for plantation forestry because it has the highest productivity of timber in those specific conditions for example. On the other hand, where light and water are abundant all year round, such as the tropics, evergreen broadleaved trees dominate (and reach great heights). Remember that are some extremely tall growing species of non-coniferous trees- Eucalyptus regnans is the second tallest tree species known.

Thanks so much sir for you valuable answers....but when productivity is more in case of broad-leaved species then why these trees are less taller than conifers...i think this may be governed by some genes....?

I don't think you can just make a general statement that broad leaved species have higher productivity but conifers are taller. There are too many exceptions. There are broadleaved trees in Tasmania that are taller than the tallest conifer here in Sweden for example. In large areas of the world broadleaved trees have lower annual productivity than conifers. Both productivity and height depend on which habitat and species we are talking about.

On the other hand, many (but not all) conifers show a high degree of apical dominance in their growth patterns, i.e. their crowns grow in height faster than in width (think of the difference in how an oak and a spruce are shaped, or on a smaller scale a tomato plant and a sunflower, even though they may have the same mass). Wood density is also an important factor- is biomass allocated in making quick vertical growth or slower growth with denser wood?

The following article is a good discussion of some of the trade offs involved in tree growth forms, in an Iberian context (and context is always important!)

Article Architecture of Iberian canopy tree species in relation to w...